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Diffstat (limited to 'dist2/doc/pcre2.txt')
| -rw-r--r-- | dist2/doc/pcre2.txt | 5600 |
1 files changed, 2579 insertions, 3021 deletions
diff --git a/dist2/doc/pcre2.txt b/dist2/doc/pcre2.txt index 9c956e8c..30ba2f9e 100644 --- a/dist2/doc/pcre2.txt +++ b/dist2/doc/pcre2.txt @@ -141,7 +141,7 @@ USER DOCUMENTATION pcre2-config show PCRE2 installation configuration information pcre2api details of PCRE2's native C API pcre2build building PCRE2 - pcre2callout details of the pattern callout feature + pcre2callout details of the callout feature pcre2compat discussion of Perl compatibility pcre2convert details of pattern conversion functions pcre2demo a demonstration C program that uses PCRE2 @@ -177,7 +177,7 @@ AUTHOR REVISION - Last updated: 17 September 2018 + Last updated: 11 July 2018 Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ @@ -293,10 +293,6 @@ PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS int (*callout_function)(pcre2_callout_block *, void *), void *callout_data); - int pcre2_set_substitute_callout(pcre2_match_context *mcontext, - int (*callout_function)(pcre2_substitute_callout_block *, void *), - void *callout_data); - int pcre2_set_offset_limit(pcre2_match_context *mcontext, PCRE2_SIZE value); @@ -402,8 +398,7 @@ PCRE2 NATIVE API AUXILIARY FUNCTIONS const unsigned char *pcre2_maketables(pcre2_general_context *gcontext); - int pcre2_pattern_info(const pcre2_code *code, uint32_t what, - void *where); + int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where); int pcre2_callout_enumerate(const pcre2_code *code, int (*callback)(pcre2_callout_enumerate_block *, void *), @@ -882,11 +877,11 @@ PCRE2 CONTEXTS int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext, uint32_t value); - This parameter adjusts the limit, set when PCRE2 is built (default - 250), on the depth of parenthesis nesting in a pattern. This limit - stops rogue patterns using up too much system stack when being com- - piled. The limit applies to parentheses of all kinds, not just captur- - ing parentheses. + This parameter ajusts the limit, set when PCRE2 is built (default 250), + on the depth of parenthesis nesting in a pattern. This limit stops + rogue patterns using up too much system stack when being compiled. The + limit applies to parentheses of all kinds, not just capturing parenthe- + ses. int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext, int (*guard_function)(uint32_t, void *), void *user_data); @@ -938,18 +933,10 @@ PCRE2 CONTEXTS int (*callout_function)(pcre2_callout_block *, void *), void *callout_data); - This sets up a callout function for PCRE2 to call at specified points + This sets up a "callout" function for PCRE2 to call at specified points during a matching operation. Details are given in the pcre2callout doc- umentation. - int pcre2_set_substitute_callout(pcre2_match_context *mcontext, - int (*callout_function)(pcre2_substitute_callout_block *, void *), - void *callout_data); - - This sets up a callout function for PCRE2 to call after each substitu- - tion made by pcre2_substitute(). Details are given in the section enti- - tled "Creating a new string with substitutions" below. - int pcre2_set_offset_limit(pcre2_match_context *mcontext, PCRE2_SIZE value); @@ -961,7 +948,7 @@ PCRE2 CONTEXTS more substitutions. For example, if the pattern /abc/ is matched against "123abc" with an - offset limit less than 3, the result is PCRE2_ERROR_NOMATCH. A match + offset limit less than 3, the result is PCRE2_ERROR_NO_MATCH. A match can never be found if the startoffset argument of pcre2_match(), pcre2_dfa_match(), or pcre2_substitute() is greater than the offset limit set in the match context. @@ -1297,68 +1284,65 @@ COMPILING A PATTERN Copies of both the code and the tables are made, with the new code pointing to the new tables. The memory for the new tables is automati- cally freed when pcre2_code_free() is called for the new copy of the - compiled code. If pcre2_code_copy_with_tables() is called with a NULL + compiled code. If pcre2_code_copy_withy_tables() is called with a NULL argument, it returns NULL. NOTE: When one of the matching functions is called, pointers to the compiled pattern and the subject string are set in the match data block - so that they can be referenced by the substring extraction functions - after a successful match. After running a match, you must not free a - compiled pattern or a subject string until after all operations on the - match data block have taken place, unless, in the case of the subject - string, you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is - described in the section entitled "Option bits for pcre2_match()" - below. - - The options argument for pcre2_compile() contains various bit settings - that affect the compilation. It should be zero if none of them are - required. The available options are described below. Some of them (in - particular, those that are compatible with Perl, but some others as - well) can also be set and unset from within the pattern (see the + so that they can be referenced by the substring extraction functions. + After running a match, you must not free a compiled pattern (or a sub- + ject string) until after all operations on the match data block have + taken place. + + The options argument for pcre2_compile() contains various bit settings + that affect the compilation. It should be zero if no options are + required. The available options are described below. Some of them (in + particular, those that are compatible with Perl, but some others as + well) can also be set and unset from within the pattern (see the detailed description in the pcre2pattern documentation). - For those options that can be different in different parts of the pat- - tern, the contents of the options argument specifies their settings at - the start of compilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and - PCRE2_NO_UTF_CHECK options can be set at the time of matching as well + For those options that can be different in different parts of the pat- + tern, the contents of the options argument specifies their settings at + the start of compilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and + PCRE2_NO_UTF_CHECK options can be set at the time of matching as well as at compile time. - Some additional options and less frequently required compile-time - parameters (for example, the newline setting) can be provided in a com- - pile context (as described above). + Other, less frequently required compile-time parameters (for example, + the newline setting) can be provided in a compile context (as described + above). If errorcode or erroroffset is NULL, pcre2_compile() returns NULL imme- - diately. Otherwise, the variables to which these point are set to an - error code and an offset (number of code units) within the pattern, - respectively, when pcre2_compile() returns NULL because a compilation + diately. Otherwise, the variables to which these point are set to an + error code and an offset (number of code units) within the pattern, + respectively, when pcre2_compile() returns NULL because a compilation error has occurred. The values are not defined when compilation is suc- cessful and pcre2_compile() returns a non-NULL value. - There are nearly 100 positive error codes that pcre2_compile() may - return if it finds an error in the pattern. There are also some nega- - tive error codes that are used for invalid UTF strings. These are the + There are nearly 100 positive error codes that pcre2_compile() may + return if it finds an error in the pattern. There are also some nega- + tive error codes that are used for invalid UTF strings. These are the same as given by pcre2_match() and pcre2_dfa_match(), and are described - in the pcre2unicode page. There is no separate documentation for the - positive error codes, because the textual error messages that are - obtained by calling the pcre2_get_error_message() function (see - "Obtaining a textual error message" below) should be self-explanatory. - Macro names starting with PCRE2_ERROR_ are defined for both positive + in the pcre2unicode page. There is no separate documentation for the + positive error codes, because the textual error messages that are + obtained by calling the pcre2_get_error_message() function (see + "Obtaining a textual error message" below) should be self-explanatory. + Macro names starting with PCRE2_ERROR_ are defined for both positive and negative error codes in pcre2.h. The value returned in erroroffset is an indication of where in the pat- - tern the error occurred. It is not necessarily the furthest point in - the pattern that was read. For example, after the error "lookbehind + tern the error occurred. It is not necessarily the furthest point in + the pattern that was read. For example, after the error "lookbehind assertion is not fixed length", the error offset points to the start of - the failing assertion. For an invalid UTF-8 or UTF-16 string, the off- + the failing assertion. For an invalid UTF-8 or UTF-16 string, the off- set is that of the first code unit of the failing character. - Some errors are not detected until the whole pattern has been scanned; - in these cases, the offset passed back is the length of the pattern. - Note that the offset is in code units, not characters, even in a UTF + Some errors are not detected until the whole pattern has been scanned; + in these cases, the offset passed back is the length of the pattern. + Note that the offset is in code units, not characters, even in a UTF mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char- acter. - This code fragment shows a typical straightforward call to pcre2_com- + This code fragment shows a typical straightforward call to pcre2_com- pile(): pcre2_code *re; @@ -1372,485 +1356,469 @@ COMPILING A PATTERN &erroffset, /* for error offset */ NULL); /* no compile context */ - - Main compile options - - The following names for option bits are defined in the pcre2.h header + The following names for option bits are defined in the pcre2.h header file: PCRE2_ANCHORED If this bit is set, the pattern is forced to be "anchored", that is, it - is constrained to match only at the first matching point in the string - that is being searched (the "subject string"). This effect can also be - achieved by appropriate constructs in the pattern itself, which is the + is constrained to match only at the first matching point in the string + that is being searched (the "subject string"). This effect can also be + achieved by appropriate constructs in the pattern itself, which is the only way to do it in Perl. PCRE2_ALLOW_EMPTY_CLASS - By default, for compatibility with Perl, a closing square bracket that - immediately follows an opening one is treated as a data character for - the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the + By default, for compatibility with Perl, a closing square bracket that + immediately follows an opening one is treated as a data character for + the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the class, which therefore contains no characters and so can never match. PCRE2_ALT_BSUX - This option request alternative handling of three escape sequences, - which makes PCRE2's behaviour more like ECMAscript (aka JavaScript). + This option request alternative handling of three escape sequences, + which makes PCRE2's behaviour more like ECMAscript (aka JavaScript). When it is set: (1) \U matches an upper case "U" character; by default \U causes a com- pile time error (Perl uses \U to upper case subsequent characters). (2) \u matches a lower case "u" character unless it is followed by four - hexadecimal digits, in which case the hexadecimal number defines the - code point to match. By default, \u causes a compile time error (Perl + hexadecimal digits, in which case the hexadecimal number defines the + code point to match. By default, \u causes a compile time error (Perl uses it to upper case the following character). - (3) \x matches a lower case "x" character unless it is followed by two - hexadecimal digits, in which case the hexadecimal number defines the - code point to match. By default, as in Perl, a hexadecimal number is + (3) \x matches a lower case "x" character unless it is followed by two + hexadecimal digits, in which case the hexadecimal number defines the + code point to match. By default, as in Perl, a hexadecimal number is always expected after \x, but it may have zero, one, or two digits (so, for example, \xz matches a binary zero character followed by z). - ECMAscript 6 added additional functionality to \u. This can be accessed - using the PCRE2_EXTRA_ALT_BSUX extra option (see "Extra compile - options" below). Note that this alternative escape handling applies - only to patterns. Neither of these options affects the processing of - replacement strings passed to pcre2_substitute(). - PCRE2_ALT_CIRCUMFLEX In multiline mode (when PCRE2_MULTILINE is set), the circumflex - metacharacter matches at the start of the subject (unless PCRE2_NOTBOL - is set), and also after any internal newline. However, it does not + metacharacter matches at the start of the subject (unless PCRE2_NOTBOL + is set), and also after any internal newline. However, it does not match after a newline at the end of the subject, for compatibility with - Perl. If you want a multiline circumflex also to match after a termi- + Perl. If you want a multiline circumflex also to match after a termi- nating newline, you must set PCRE2_ALT_CIRCUMFLEX. PCRE2_ALT_VERBNAMES - By default, for compatibility with Perl, the name in any verb sequence - such as (*MARK:NAME) is any sequence of characters that does not - include a closing parenthesis. The name is not processed in any way, - and it is not possible to include a closing parenthesis in the name. - However, if the PCRE2_ALT_VERBNAMES option is set, normal backslash - processing is applied to verb names and only an unescaped closing - parenthesis terminates the name. A closing parenthesis can be included - in a name either as \) or between \Q and \E. If the PCRE2_EXTENDED or - PCRE2_EXTENDED_MORE option is set with PCRE2_ALT_VERBNAMES, unescaped - whitespace in verb names is skipped and #-comments are recognized, + By default, for compatibility with Perl, the name in any verb sequence + such as (*MARK:NAME) is any sequence of characters that does not + include a closing parenthesis. The name is not processed in any way, + and it is not possible to include a closing parenthesis in the name. + However, if the PCRE2_ALT_VERBNAMES option is set, normal backslash + processing is applied to verb names and only an unescaped closing + parenthesis terminates the name. A closing parenthesis can be included + in a name either as \) or between \Q and \E. If the PCRE2_EXTENDED or + PCRE2_EXTENDED_MORE option is set with PCRE2_ALT_VERBNAMES, unescaped + whitespace in verb names is skipped and #-comments are recognized, exactly as in the rest of the pattern. PCRE2_AUTO_CALLOUT - If this bit is set, pcre2_compile() automatically inserts callout - items, all with number 255, before each pattern item, except immedi- - ately before or after an explicit callout in the pattern. For discus- + If this bit is set, pcre2_compile() automatically inserts callout + items, all with number 255, before each pattern item, except immedi- + ately before or after an explicit callout in the pattern. For discus- sion of the callout facility, see the pcre2callout documentation. PCRE2_CASELESS - If this bit is set, letters in the pattern match both upper and lower - case letters in the subject. It is equivalent to Perl's /i option, and - it can be changed within a pattern by a (?i) option setting. If - PCRE2_UTF is set, Unicode properties are used for all characters with - more than one other case, and for all characters whose code points are - greater than U+007F. For lower valued characters with only one other - case, a lookup table is used for speed. When PCRE2_UTF is not set, a + If this bit is set, letters in the pattern match both upper and lower + case letters in the subject. It is equivalent to Perl's /i option, and + it can be changed within a pattern by a (?i) option setting. If + PCRE2_UTF is set, Unicode properties are used for all characters with + more than one other case, and for all characters whose code points are + greater than U+007F. For lower valued characters with only one other + case, a lookup table is used for speed. When PCRE2_UTF is not set, a lookup table is used for all code points less than 256, and higher code - points (available only in 16-bit or 32-bit mode) are treated as not + points (available only in 16-bit or 32-bit mode) are treated as not having another case. PCRE2_DOLLAR_ENDONLY - If this bit is set, a dollar metacharacter in the pattern matches only - at the end of the subject string. Without this option, a dollar also - matches immediately before a newline at the end of the string (but not - before any other newlines). The PCRE2_DOLLAR_ENDONLY option is ignored - if PCRE2_MULTILINE is set. There is no equivalent to this option in + If this bit is set, a dollar metacharacter in the pattern matches only + at the end of the subject string. Without this option, a dollar also + matches immediately before a newline at the end of the string (but not + before any other newlines). The PCRE2_DOLLAR_ENDONLY option is ignored + if PCRE2_MULTILINE is set. There is no equivalent to this option in Perl, and no way to set it within a pattern. PCRE2_DOTALL - If this bit is set, a dot metacharacter in the pattern matches any - character, including one that indicates a newline. However, it only + If this bit is set, a dot metacharacter in the pattern matches any + character, including one that indicates a newline. However, it only ever matches one character, even if newlines are coded as CRLF. Without this option, a dot does not match when the current position in the sub- - ject is at a newline. This option is equivalent to Perl's /s option, + ject is at a newline. This option is equivalent to Perl's /s option, and it can be changed within a pattern by a (?s) option setting. A neg- - ative class such as [^a] always matches newline characters, and the \N - escape sequence always matches a non-newline character, independent of + ative class such as [^a] always matches newline characters, and the \N + escape sequence always matches a non-newline character, independent of the setting of PCRE2_DOTALL. PCRE2_DUPNAMES - If this bit is set, names used to identify capture groups need not be - unique. This can be helpful for certain types of pattern when it is - known that only one instance of the named group can ever be matched. - There are more details of named capture groups below; see also the - pcre2pattern documentation. + If this bit is set, names used to identify capturing subpatterns need + not be unique. This can be helpful for certain types of pattern when it + is known that only one instance of the named subpattern can ever be + matched. There are more details of named subpatterns below; see also + the pcre2pattern documentation. PCRE2_ENDANCHORED - If this bit is set, the end of any pattern match must be right at the + If this bit is set, the end of any pattern match must be right at the end of the string being searched (the "subject string"). If the pattern match succeeds by reaching (*ACCEPT), but does not reach the end of the - subject, the match fails at the current starting point. For unanchored - patterns, a new match is then tried at the next starting point. How- + subject, the match fails at the current starting point. For unanchored + patterns, a new match is then tried at the next starting point. How- ever, if the match succeeds by reaching the end of the pattern, but not - the end of the subject, backtracking occurs and an alternative match + the end of the subject, backtracking occurs and an alternative match may be found. Consider these two patterns: .(*ACCEPT)|.. .|.. - If matched against "abc" with PCRE2_ENDANCHORED set, the first matches - "c" whereas the second matches "bc". The effect of PCRE2_ENDANCHORED - can also be achieved by appropriate constructs in the pattern itself, + If matched against "abc" with PCRE2_ENDANCHORED set, the first matches + "c" whereas the second matches "bc". The effect of PCRE2_ENDANCHORED + can also be achieved by appropriate constructs in the pattern itself, which is the only way to do it in Perl. For DFA matching with pcre2_dfa_match(), PCRE2_ENDANCHORED applies only - to the first (that is, the longest) matched string. Other parallel - matches, which are necessarily substrings of the first one, must obvi- + to the first (that is, the longest) matched string. Other parallel + matches, which are necessarily substrings of the first one, must obvi- ously end before the end of the subject. PCRE2_EXTENDED - If this bit is set, most white space characters in the pattern are - totally ignored except when escaped or inside a character class. How- - ever, white space is not allowed within sequences such as (?> that - introduce various parenthesized groups, nor within numerical quanti- - fiers such as {1,3}. Ignorable white space is permitted between an item - and a following quantifier and between a quantifier and a following + - that indicates possessiveness. PCRE2_EXTENDED is equivalent to Perl's - /x option, and it can be changed within a pattern by a (?x) option set- - ting. - - When PCRE2 is compiled without Unicode support, PCRE2_EXTENDED recog- - nizes as white space only those characters with code points less than + If this bit is set, most white space characters in the pattern are + totally ignored except when escaped or inside a character class. How- + ever, white space is not allowed within sequences such as (?> that + introduce various parenthesized subpatterns, nor within numerical quan- + tifiers such as {1,3}. Ignorable white space is permitted between an + item and a following quantifier and between a quantifier and a follow- + ing + that indicates possessiveness. PCRE2_EXTENDED is equivalent to + Perl's /x option, and it can be changed within a pattern by a (?x) + option setting. + + When PCRE2 is compiled without Unicode support, PCRE2_EXTENDED recog- + nizes as white space only those characters with code points less than 256 that are flagged as white space in its low-character table. The ta- ble is normally created by pcre2_maketables(), which uses the isspace() - function to identify space characters. In most ASCII environments, the - relevant characters are those with code points 0x0009 (tab), 0x000A - (linefeed), 0x000B (vertical tab), 0x000C (formfeed), 0x000D (carriage + function to identify space characters. In most ASCII environments, the + relevant characters are those with code points 0x0009 (tab), 0x000A + (linefeed), 0x000B (vertical tab), 0x000C (formfeed), 0x000D (carriage return), and 0x0020 (space). When PCRE2 is compiled with Unicode support, in addition to these char- - acters, five more Unicode "Pattern White Space" characters are recog- + acters, five more Unicode "Pattern White Space" characters are recog- nized by PCRE2_EXTENDED. These are U+0085 (next line), U+200E (left-to- - right mark), U+200F (right-to-left mark), U+2028 (line separator), and - U+2029 (paragraph separator). This set of characters is the same as - recognized by Perl's /x option. Note that the horizontal and vertical - space characters that are matched by the \h and \v escapes in patterns + right mark), U+200F (right-to-left mark), U+2028 (line separator), and + U+2029 (paragraph separator). This set of characters is the same as + recognized by Perl's /x option. Note that the horizontal and vertical + space characters that are matched by the \h and \v escapes in patterns are a much bigger set. - As well as ignoring most white space, PCRE2_EXTENDED also causes char- - acters between an unescaped # outside a character class and the next - newline, inclusive, to be ignored, which makes it possible to include + As well as ignoring most white space, PCRE2_EXTENDED also causes char- + acters between an unescaped # outside a character class and the next + newline, inclusive, to be ignored, which makes it possible to include comments inside complicated patterns. Note that the end of this type of - comment is a literal newline sequence in the pattern; escape sequences + comment is a literal newline sequence in the pattern; escape sequences that happen to represent a newline do not count. Which characters are interpreted as newlines can be specified by a set- - ting in the compile context that is passed to pcre2_compile() or by a - special sequence at the start of the pattern, as described in the sec- - tion entitled "Newline conventions" in the pcre2pattern documentation. + ting in the compile context that is passed to pcre2_compile() or by a + special sequence at the start of the pattern, as described in the sec- + tion entitled "Newline conventions" in the pcre2pattern documentation. A default is defined when PCRE2 is built. PCRE2_EXTENDED_MORE - This option has the effect of PCRE2_EXTENDED, but, in addition, - unescaped space and horizontal tab characters are ignored inside a - character class. Note: only these two characters are ignored, not the - full set of pattern white space characters that are ignored outside a + This option has the effect of PCRE2_EXTENDED, but, in addition, + unescaped space and horizontal tab characters are ignored inside a + character class. Note: only these two characters are ignored, not the + full set of pattern white space characters that are ignored outside a character class. PCRE2_EXTENDED_MORE is equivalent to Perl's /xx - option, and it can be changed within a pattern by a (?xx) option set- + option, and it can be changed within a pattern by a (?xx) option set- ting. PCRE2_FIRSTLINE If this option is set, the start of an unanchored pattern match must be - before or at the first newline in the subject string following the - start of matching, though the matched text may continue over the new- + before or at the first newline in the subject string following the + start of matching, though the matched text may continue over the new- line. If startoffset is non-zero, the limiting newline is not necessar- - ily the first newline in the subject. For example, if the subject + ily the first newline in the subject. For example, if the subject string is "abc\nxyz" (where \n represents a single-character newline) a - pattern match for "yz" succeeds with PCRE2_FIRSTLINE if startoffset is - greater than 3. See also PCRE2_USE_OFFSET_LIMIT, which provides a more - general limiting facility. If PCRE2_FIRSTLINE is set with an offset - limit, a match must occur in the first line and also within the offset + pattern match for "yz" succeeds with PCRE2_FIRSTLINE if startoffset is + greater than 3. See also PCRE2_USE_OFFSET_LIMIT, which provides a more + general limiting facility. If PCRE2_FIRSTLINE is set with an offset + limit, a match must occur in the first line and also within the offset limit. In other words, whichever limit comes first is used. PCRE2_LITERAL If this option is set, all meta-characters in the pattern are disabled, - and it is treated as a literal string. Matching literal strings with a + and it is treated as a literal string. Matching literal strings with a regular expression engine is not the most efficient way of doing it. If - you are doing a lot of literal matching and are worried about effi- + you are doing a lot of literal matching and are worried about effi- ciency, you should consider using other approaches. The only other main options that are allowed with PCRE2_LITERAL are: PCRE2_ANCHORED, PCRE2_ENDANCHORED, PCRE2_AUTO_CALLOUT, PCRE2_CASELESS, PCRE2_FIRSTLINE, PCRE2_NO_START_OPTIMIZE, PCRE2_NO_UTF_CHECK, PCRE2_UTF, and - PCRE2_USE_OFFSET_LIMIT. The extra options PCRE2_EXTRA_MATCH_LINE and - PCRE2_EXTRA_MATCH_WORD are also supported. Any other options cause an + PCRE2_USE_OFFSET_LIMIT. The extra options PCRE2_EXTRA_MATCH_LINE and + PCRE2_EXTRA_MATCH_WORD are also supported. Any other options cause an error. PCRE2_MATCH_UNSET_BACKREF - If this option is set, a backreference to an unset capture group - matches an empty string (by default this causes the current matching - alternative to fail). A pattern such as (\1)(a) succeeds when this - option is set (assuming it can find an "a" in the subject), whereas it - fails by default, for Perl compatibility. Setting this option makes + If this option is set, a backreference to an unset subpattern group + matches an empty string (by default this causes the current matching + alternative to fail). A pattern such as (\1)(a) succeeds when this + option is set (assuming it can find an "a" in the subject), whereas it + fails by default, for Perl compatibility. Setting this option makes PCRE2 behave more like ECMAscript (aka JavaScript). PCRE2_MULTILINE - By default, for the purposes of matching "start of line" and "end of - line", PCRE2 treats the subject string as consisting of a single line - of characters, even if it actually contains newlines. The "start of - line" metacharacter (^) matches only at the start of the string, and - the "end of line" metacharacter ($) matches only at the end of the + By default, for the purposes of matching "start of line" and "end of + line", PCRE2 treats the subject string as consisting of a single line + of characters, even if it actually contains newlines. The "start of + line" metacharacter (^) matches only at the start of the string, and + the "end of line" metacharacter ($) matches only at the end of the string, or before a terminating newline (except when PCRE2_DOL- - LAR_ENDONLY is set). Note, however, that unless PCRE2_DOTALL is set, + LAR_ENDONLY is set). Note, however, that unless PCRE2_DOTALL is set, the "any character" metacharacter (.) does not match at a newline. This behaviour (for ^, $, and dot) is the same as Perl. - When PCRE2_MULTILINE it is set, the "start of line" and "end of line" - constructs match immediately following or immediately before internal - newlines in the subject string, respectively, as well as at the very - start and end. This is equivalent to Perl's /m option, and it can be + When PCRE2_MULTILINE it is set, the "start of line" and "end of line" + constructs match immediately following or immediately before internal + newlines in the subject string, respectively, as well as at the very + start and end. This is equivalent to Perl's /m option, and it can be changed within a pattern by a (?m) option setting. Note that the "start of line" metacharacter does not match after a newline at the end of the - subject, for compatibility with Perl. However, you can change this by - setting the PCRE2_ALT_CIRCUMFLEX option. If there are no newlines in a - subject string, or no occurrences of ^ or $ in a pattern, setting + subject, for compatibility with Perl. However, you can change this by + setting the PCRE2_ALT_CIRCUMFLEX option. If there are no newlines in a + subject string, or no occurrences of ^ or $ in a pattern, setting PCRE2_MULTILINE has no effect. PCRE2_NEVER_BACKSLASH_C - This option locks out the use of \C in the pattern that is being com- - piled. This escape can cause unpredictable behaviour in UTF-8 or - UTF-16 modes, because it may leave the current matching point in the - middle of a multi-code-unit character. This option may be useful in - applications that process patterns from external sources. Note that + This option locks out the use of \C in the pattern that is being com- + piled. This escape can cause unpredictable behaviour in UTF-8 or + UTF-16 modes, because it may leave the current matching point in the + middle of a multi-code-unit character. This option may be useful in + applications that process patterns from external sources. Note that there is also a build-time option that permanently locks out the use of \C. PCRE2_NEVER_UCP - This option locks out the use of Unicode properties for handling \B, + This option locks out the use of Unicode properties for handling \B, \b, \D, \d, \S, \s, \W, \w, and some of the POSIX character classes, as - described for the PCRE2_UCP option below. In particular, it prevents - the creator of the pattern from enabling this facility by starting the - pattern with (*UCP). This option may be useful in applications that + described for the PCRE2_UCP option below. In particular, it prevents + the creator of the pattern from enabling this facility by starting the + pattern with (*UCP). This option may be useful in applications that process patterns from external sources. The option combination PCRE_UCP and PCRE_NEVER_UCP causes an error. PCRE2_NEVER_UTF - This option locks out interpretation of the pattern as UTF-8, UTF-16, + This option locks out interpretation of the pattern as UTF-8, UTF-16, or UTF-32, depending on which library is in use. In particular, it pre- - vents the creator of the pattern from switching to UTF interpretation - by starting the pattern with (*UTF). This option may be useful in - applications that process patterns from external sources. The combina- + vents the creator of the pattern from switching to UTF interpretation + by starting the pattern with (*UTF). This option may be useful in + applications that process patterns from external sources. The combina- tion of PCRE2_UTF and PCRE2_NEVER_UTF causes an error. PCRE2_NO_AUTO_CAPTURE If this option is set, it disables the use of numbered capturing paren- - theses in the pattern. Any opening parenthesis that is not followed by - ? behaves as if it were followed by ?: but named parentheses can still + theses in the pattern. Any opening parenthesis that is not followed by + ? behaves as if it were followed by ?: but named parentheses can still be used for capturing (and they acquire numbers in the usual way). This - is the same as Perl's /n option. Note that, when this option is set, - references to capture groups (backreferences or recursion/subroutine - calls) may only refer to named groups, though the reference can be by + is the same as Perl's /n option. Note that, when this option is set, + references to capturing groups (backreferences or recursion/subroutine + calls) may only refer to named groups, though the reference can be by name or by number. PCRE2_NO_AUTO_POSSESS If this option is set, it disables "auto-possessification", which is an - optimization that, for example, turns a+b into a++b in order to avoid - backtracks into a+ that can never be successful. However, if callouts - are in use, auto-possessification means that some callouts are never + optimization that, for example, turns a+b into a++b in order to avoid + backtracks into a+ that can never be successful. However, if callouts + are in use, auto-possessification means that some callouts are never taken. You can set this option if you want the matching functions to do - a full unoptimized search and run all the callouts, but it is mainly + a full unoptimized search and run all the callouts, but it is mainly provided for testing purposes. PCRE2_NO_DOTSTAR_ANCHOR If this option is set, it disables an optimization that is applied when - .* is the first significant item in a top-level branch of a pattern, - and all the other branches also start with .* or with \A or \G or ^. - The optimization is automatically disabled for .* if it is inside an - atomic group or a capture group that is the subject of a backreference, - or if the pattern contains (*PRUNE) or (*SKIP). When the optimization - is not disabled, such a pattern is automatically anchored if + .* is the first significant item in a top-level branch of a pattern, + and all the other branches also start with .* or with \A or \G or ^. + The optimization is automatically disabled for .* if it is inside an + atomic group or a capturing group that is the subject of a backrefer- + ence, or if the pattern contains (*PRUNE) or (*SKIP). When the opti- + mization is not disabled, such a pattern is automatically anchored if PCRE2_DOTALL is set for all the .* items and PCRE2_MULTILINE is not set - for any ^ items. Otherwise, the fact that any match must start either - at the start of the subject or following a newline is remembered. Like + for any ^ items. Otherwise, the fact that any match must start either + at the start of the subject or following a newline is remembered. Like other optimizations, this can cause callouts to be skipped. PCRE2_NO_START_OPTIMIZE - This is an option whose main effect is at matching time. It does not + This is an option whose main effect is at matching time. It does not change what pcre2_compile() generates, but it does affect the output of the JIT compiler. - There are a number of optimizations that may occur at the start of a - match, in order to speed up the process. For example, if it is known - that an unanchored match must start with a specific code unit value, - the matching code searches the subject for that value, and fails imme- - diately if it cannot find it, without actually running the main match- - ing function. This means that a special item such as (*COMMIT) at the - start of a pattern is not considered until after a suitable starting - point for the match has been found. Also, when callouts or (*MARK) - items are in use, these "start-up" optimizations can cause them to be - skipped if the pattern is never actually used. The start-up optimiza- - tions are in effect a pre-scan of the subject that takes place before + There are a number of optimizations that may occur at the start of a + match, in order to speed up the process. For example, if it is known + that an unanchored match must start with a specific code unit value, + the matching code searches the subject for that value, and fails imme- + diately if it cannot find it, without actually running the main match- + ing function. This means that a special item such as (*COMMIT) at the + start of a pattern is not considered until after a suitable starting + point for the match has been found. Also, when callouts or (*MARK) + items are in use, these "start-up" optimizations can cause them to be + skipped if the pattern is never actually used. The start-up optimiza- + tions are in effect a pre-scan of the subject that takes place before the pattern is run. The PCRE2_NO_START_OPTIMIZE option disables the start-up optimizations, - possibly causing performance to suffer, but ensuring that in cases - where the result is "no match", the callouts do occur, and that items + possibly causing performance to suffer, but ensuring that in cases + where the result is "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK) are considered at every possible starting position in the subject string. - Setting PCRE2_NO_START_OPTIMIZE may change the outcome of a matching + Setting PCRE2_NO_START_OPTIMIZE may change the outcome of a matching operation. Consider the pattern (*COMMIT)ABC - When this is compiled, PCRE2 records the fact that a match must start - with the character "A". Suppose the subject string is "DEFABC". The - start-up optimization scans along the subject, finds "A" and runs the - first match attempt from there. The (*COMMIT) item means that the pat- - tern must match the current starting position, which in this case, it - does. However, if the same match is run with PCRE2_NO_START_OPTIMIZE - set, the initial scan along the subject string does not happen. The - first match attempt is run starting from "D" and when this fails, - (*COMMIT) prevents any further matches being tried, so the overall + When this is compiled, PCRE2 records the fact that a match must start + with the character "A". Suppose the subject string is "DEFABC". The + start-up optimization scans along the subject, finds "A" and runs the + first match attempt from there. The (*COMMIT) item means that the pat- + tern must match the current starting position, which in this case, it + does. However, if the same match is run with PCRE2_NO_START_OPTIMIZE + set, the initial scan along the subject string does not happen. The + first match attempt is run starting from "D" and when this fails, + (*COMMIT) prevents any further matches being tried, so the overall result is "no match". - There are also other start-up optimizations. For example, a minimum + There are also other start-up optimizations. For example, a minimum length for the subject may be recorded. Consider the pattern (*MARK:A)(X|Y) - The minimum length for a match is one character. If the subject is + The minimum length for a match is one character. If the subject is "ABC", there will be attempts to match "ABC", "BC", and "C". An attempt to match an empty string at the end of the subject does not take place, - because PCRE2 knows that the subject is now too short, and so the - (*MARK) is never encountered. In this case, the optimization does not + because PCRE2 knows that the subject is now too short, and so the + (*MARK) is never encountered. In this case, the optimization does not affect the overall match result, which is still "no match", but it does affect the auxiliary information that is returned. PCRE2_NO_UTF_CHECK - When PCRE2_UTF is set, the validity of the pattern as a UTF string is - automatically checked. There are discussions about the validity of - UTF-8 strings, UTF-16 strings, and UTF-32 strings in the pcre2unicode - document. If an invalid UTF sequence is found, pcre2_compile() returns + When PCRE2_UTF is set, the validity of the pattern as a UTF string is + automatically checked. There are discussions about the validity of + UTF-8 strings, UTF-16 strings, and UTF-32 strings in the pcre2unicode + document. If an invalid UTF sequence is found, pcre2_compile() returns a negative error code. - If you know that your pattern is a valid UTF string, and you want to - skip this check for performance reasons, you can set the - PCRE2_NO_UTF_CHECK option. When it is set, the effect of passing an + If you know that your pattern is a valid UTF string, and you want to + skip this check for performance reasons, you can set the + PCRE2_NO_UTF_CHECK option. When it is set, the effect of passing an invalid UTF string as a pattern is undefined. It may cause your program to crash or loop. Note that this option can also be passed to pcre2_match() and - pcre_dfa_match(), to suppress UTF validity checking of the subject + pcre_dfa_match(), to suppress UTF validity checking of the subject string. Note also that setting PCRE2_NO_UTF_CHECK at compile time does not dis- - able the error that is given if an escape sequence for an invalid Uni- - code code point is encountered in the pattern. In particular, the so- - called "surrogate" code points (0xd800 to 0xdfff) are invalid. If you - want to allow escape sequences such as \x{d800} you can set the - PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extra option, as described in the - section entitled "Extra compile options" below. However, this is pos- + able the error that is given if an escape sequence for an invalid Uni- + code code point is encountered in the pattern. In particular, the so- + called "surrogate" code points (0xd800 to 0xdfff) are invalid. If you + want to allow escape sequences such as \x{d800} you can set the + PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extra option, as described in the + section entitled "Extra compile options" below. However, this is pos- sible only in UTF-8 and UTF-32 modes, because these values are not rep- resentable in UTF-16. PCRE2_UCP This option changes the way PCRE2 processes \B, \b, \D, \d, \S, \s, \W, - \w, and some of the POSIX character classes. By default, only ASCII - characters are recognized, but if PCRE2_UCP is set, Unicode properties - are used instead to classify characters. More details are given in the + \w, and some of the POSIX character classes. By default, only ASCII + characters are recognized, but if PCRE2_UCP is set, Unicode properties + are used instead to classify characters. More details are given in the section on generic character types in the pcre2pattern page. If you set - PCRE2_UCP, matching one of the items it affects takes much longer. The - option is available only if PCRE2 has been compiled with Unicode sup- + PCRE2_UCP, matching one of the items it affects takes much longer. The + option is available only if PCRE2 has been compiled with Unicode sup- port (which is the default). PCRE2_UNGREEDY - This option inverts the "greediness" of the quantifiers so that they - are not greedy by default, but become greedy if followed by "?". It is - not compatible with Perl. It can also be set by a (?U) option setting + This option inverts the "greediness" of the quantifiers so that they + are not greedy by default, but become greedy if followed by "?". It is + not compatible with Perl. It can also be set by a (?U) option setting within the pattern. PCRE2_USE_OFFSET_LIMIT This option must be set for pcre2_compile() if pcre2_set_offset_limit() - is going to be used to set a non-default offset limit in a match con- - text for matches that use this pattern. An error is generated if an - offset limit is set without this option. For more details, see the - description of pcre2_set_offset_limit() in the section that describes + is going to be used to set a non-default offset limit in a match con- + text for matches that use this pattern. An error is generated if an + offset limit is set without this option. For more details, see the + description of pcre2_set_offset_limit() in the section that describes match contexts. See also the PCRE2_FIRSTLINE option above. PCRE2_UTF - This option causes PCRE2 to regard both the pattern and the subject - strings that are subsequently processed as strings of UTF characters - instead of single-code-unit strings. It is available when PCRE2 is - built to include Unicode support (which is the default). If Unicode - support is not available, the use of this option provokes an error. - Details of how PCRE2_UTF changes the behaviour of PCRE2 are given in - the pcre2unicode page. In particular, note that it changes the way + This option causes PCRE2 to regard both the pattern and the subject + strings that are subsequently processed as strings of UTF characters + instead of single-code-unit strings. It is available when PCRE2 is + built to include Unicode support (which is the default). If Unicode + support is not available, the use of this option provokes an error. + Details of how PCRE2_UTF changes the behaviour of PCRE2 are given in + the pcre2unicode page. In particular, note that it changes the way PCRE2_CASELESS handles characters with code points greater than 127. Extra compile options - The option bits that can be set in a compile context by calling the - pcre2_set_compile_extra_options() function are as follows: + Unlike the main compile-time options, the extra options are not saved + with the compiled pattern. The option bits that can be set in a compile + context by calling the pcre2_set_compile_extra_options() function are + as follows: PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES - This option applies when compiling a pattern in UTF-8 or UTF-32 mode. - It is forbidden in UTF-16 mode, and ignored in non-UTF modes. Unicode + This option applies when compiling a pattern in UTF-8 or UTF-32 mode. + It is forbidden in UTF-16 mode, and ignored in non-UTF modes. Unicode "surrogate" code points in the range 0xd800 to 0xdfff are used in pairs - in UTF-16 to encode code points with values in the range 0x10000 to - 0x10ffff. The surrogates cannot therefore be represented in UTF-16. + in UTF-16 to encode code points with values in the range 0x10000 to + 0x10ffff. The surrogates cannot therefore be represented in UTF-16. They can be represented in UTF-8 and UTF-32, but are defined as invalid - code points, and cause errors if encountered in a UTF-8 or UTF-32 + code points, and cause errors if encountered in a UTF-8 or UTF-32 string that is being checked for validity by PCRE2. - These values also cause errors if encountered in escape sequences such + These values also cause errors if encountered in escape sequences such as \x{d912} within a pattern. However, it seems that some applications, - when using PCRE2 to check for unwanted characters in UTF-8 strings, - explicitly test for the surrogates using escape sequences. The - PCRE2_NO_UTF_CHECK option does not disable the error that occurs, - because it applies only to the testing of input strings for UTF valid- + when using PCRE2 to check for unwanted characters in UTF-8 strings, + explicitly test for the surrogates using escape sequences. The + PCRE2_NO_UTF_CHECK option does not disable the error that occurs, + because it applies only to the testing of input strings for UTF valid- ity. - If the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set, surro- - gate code point values in UTF-8 and UTF-32 patterns no longer provoke - errors and are incorporated in the compiled pattern. However, they can - only match subject characters if the matching function is called with + If the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set, surro- + gate code point values in UTF-8 and UTF-32 patterns no longer provoke + errors and are incorporated in the compiled pattern. However, they can + only match subject characters if the matching function is called with PCRE2_NO_UTF_CHECK set. - PCRE2_EXTRA_ALT_BSUX - - The original option PCRE2_ALT_BSUX causes PCRE2 to process \U, \u, and - \x in the way that ECMAscript (aka JavaScript) does. Additional func- - tionality was defined by ECMAscript 6; setting PCRE2_EXTRA_ALT_BSUX has - the effect of PCRE2_ALT_BSUX, but in addition it recognizes \u{hhh..} - as a hexadecimal character code, where hhh.. is any number of hexadeci- - mal digits. - PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL This is a dangerous option. Use with care. By default, an unrecognized @@ -1863,41 +1831,28 @@ COMPILING A PATTERN Perl. If the PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL extra option is passed to - pcre2_compile(), all unrecognized or malformed escape sequences are + pcre2_compile(), all unrecognized or erroneous escape sequences are treated as single-character escapes. For example, \j is a literal "j" and \x{2z} is treated as the literal string "x{2z}". Setting this option means that typos in patterns may go undetected and have unex- - pected results. Also note that a sequence such as [\N{] is interpreted - as a malformed attempt at [\N{...}] and so is treated as [N{] whereas - [\N] gives an error because an unqualified \N is a valid escape - sequence but is not supported in a character class. To reiterate: this - is a dangerous option. Use with great care. - - PCRE2_EXTRA_ESCAPED_CR_IS_LF - - There are some legacy applications where the escape sequence \r in a - pattern is expected to match a newline. If this option is set, \r in a - pattern is converted to \n so that it matches a LF (linefeed) instead - of a CR (carriage return) character. The option does not affect a lit- - eral CR in the pattern, nor does it affect CR specified as an explicit - code point such as \x{0D}. + pected results. This is a dangerous option. Use with care. PCRE2_EXTRA_MATCH_LINE - This option is provided for use by the -x option of pcre2grep. It - causes the pattern only to match complete lines. This is achieved by - automatically inserting the code for "^(?:" at the start of the com- - piled pattern and ")$" at the end. Thus, when PCRE2_MULTILINE is set, - the matched line may be in the middle of the subject string. This + This option is provided for use by the -x option of pcre2grep. It + causes the pattern only to match complete lines. This is achieved by + automatically inserting the code for "^(?:" at the start of the com- + piled pattern and ")$" at the end. Thus, when PCRE2_MULTILINE is set, + the matched line may be in the middle of the subject string. This option can be used with PCRE2_LITERAL. PCRE2_EXTRA_MATCH_WORD - This option is provided for use by the -w option of pcre2grep. It - causes the pattern only to match strings that have a word boundary at - the start and the end. This is achieved by automatically inserting the - code for "\b(?:" at the start of the compiled pattern and ")\b" at the - end. The option may be used with PCRE2_LITERAL. However, it is ignored + This option is provided for use by the -w option of pcre2grep. It + causes the pattern only to match strings that have a word boundary at + the start and the end. This is achieved by automatically inserting the + code for "\b(?:" at the start of the compiled pattern and ")\b" at the + end. The option may be used with PCRE2_LITERAL. However, it is ignored if PCRE2_EXTRA_MATCH_LINE is also set. @@ -1920,53 +1875,53 @@ JUST-IN-TIME (JIT) COMPILATION void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack); - These functions provide support for JIT compilation, which, if the - just-in-time compiler is available, further processes a compiled pat- + These functions provide support for JIT compilation, which, if the + just-in-time compiler is available, further processes a compiled pat- tern into machine code that executes much faster than the pcre2_match() - interpretive matching function. Full details are given in the pcre2jit + interpretive matching function. Full details are given in the pcre2jit documentation. - JIT compilation is a heavyweight optimization. It can take some time - for patterns to be analyzed, and for one-off matches and simple pat- - terns the benefit of faster execution might be offset by a much slower - compilation time. Most (but not all) patterns can be optimized by the + JIT compilation is a heavyweight optimization. It can take some time + for patterns to be analyzed, and for one-off matches and simple pat- + terns the benefit of faster execution might be offset by a much slower + compilation time. Most (but not all) patterns can be optimized by the JIT compiler. LOCALE SUPPORT - PCRE2 handles caseless matching, and determines whether characters are - letters, digits, or whatever, by reference to a set of tables, indexed - by character code point. This applies only to characters whose code - points are less than 256. By default, higher-valued code points never - match escapes such as \w or \d. However, if PCRE2 is built with Uni- + PCRE2 handles caseless matching, and determines whether characters are + letters, digits, or whatever, by reference to a set of tables, indexed + by character code point. This applies only to characters whose code + points are less than 256. By default, higher-valued code points never + match escapes such as \w or \d. However, if PCRE2 is built with Uni- code support, all characters can be tested with \p and \P, or, alterna- - tively, the PCRE2_UCP option can be set when a pattern is compiled; - this causes \w and friends to use Unicode property support instead of + tively, the PCRE2_UCP option can be set when a pattern is compiled; + this causes \w and friends to use Unicode property support instead of the built-in tables. - The use of locales with Unicode is discouraged. If you are handling - characters with code points greater than 128, you should either use + The use of locales with Unicode is discouraged. If you are handling + characters with code points greater than 128, you should either use Unicode support, or use locales, but not try to mix the two. - PCRE2 contains an internal set of character tables that are used by - default. These are sufficient for many applications. Normally, the + PCRE2 contains an internal set of character tables that are used by + default. These are sufficient for many applications. Normally, the internal tables recognize only ASCII characters. However, when PCRE2 is built, it is possible to cause the internal tables to be rebuilt in the default "C" locale of the local system, which may cause them to be dif- ferent. - The internal tables can be overridden by tables supplied by the appli- - cation that calls PCRE2. These may be created in a different locale - from the default. As more and more applications change to using Uni- + The internal tables can be overridden by tables supplied by the appli- + cation that calls PCRE2. These may be created in a different locale + from the default. As more and more applications change to using Uni- code, the need for this locale support is expected to die away. - External tables are built by calling the pcre2_maketables() function, - in the relevant locale. The result can be passed to pcre2_compile() as - often as necessary, by creating a compile context and calling - pcre2_set_character_tables() to set the tables pointer therein. For - example, to build and use tables that are appropriate for the French - locale (where accented characters with values greater than 128 are + External tables are built by calling the pcre2_maketables() function, + in the relevant locale. The result can be passed to pcre2_compile() as + often as necessary, by creating a compile context and calling + pcre2_set_character_tables() to set the tables pointer therein. For + example, to build and use tables that are appropriate for the French + locale (where accented characters with values greater than 128 are treated as letters), the following code could be used: setlocale(LC_CTYPE, "fr_FR"); @@ -1975,15 +1930,15 @@ LOCALE SUPPORT pcre2_set_character_tables(ccontext, tables); re = pcre2_compile(..., ccontext); - The locale name "fr_FR" is used on Linux and other Unix-like systems; - if you are using Windows, the name for the French locale is "french". - It is the caller's responsibility to ensure that the memory containing + The locale name "fr_FR" is used on Linux and other Unix-like systems; + if you are using Windows, the name for the French locale is "french". + It is the caller's responsibility to ensure that the memory containing the tables remains available for as long as it is needed. The pointer that is passed (via the compile context) to pcre2_compile() - is saved with the compiled pattern, and the same tables are used by - pcre2_match() and pcre_dfa_match(). Thus, for any single pattern, com- - pilation and matching both happen in the same locale, but different + is saved with the compiled pattern, and the same tables are used by + pcre2_match() and pcre_dfa_match(). Thus, for any single pattern, com- + pilation and matching both happen in the same locale, but different patterns can be processed in different locales. @@ -1991,13 +1946,13 @@ INFORMATION ABOUT A COMPILED PATTERN int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where); - The pcre2_pattern_info() function returns general information about a + The pcre2_pattern_info() function returns general information about a compiled pattern. For information about callouts, see the next section. - The first argument for pcre2_pattern_info() is a pointer to the com- + The first argument for pcre2_pattern_info() is a pointer to the com- piled pattern. The second argument specifies which piece of information - is required, and the third argument is a pointer to a variable to - receive the data. If the third argument is NULL, the first argument is - ignored, and the function returns the size in bytes of the variable + is required, and the third argument is a pointer to a variable to + receive the data. If the third argument is NULL, the first argument is + ignored, and the function returns the size in bytes of the variable that is required for the information requested. Otherwise, the yield of the function is zero for success, or one of the following negative num- bers: @@ -2007,9 +1962,9 @@ INFORMATION ABOUT A COMPILED PATTERN PCRE2_ERROR_BADOPTION the value of what was invalid PCRE2_ERROR_UNSET the requested field is not set - The "magic number" is placed at the start of each compiled pattern as - an simple check against passing an arbitrary memory pointer. Here is a - typical call of pcre2_pattern_info(), to obtain the length of the com- + The "magic number" is placed at the start of each compiled pattern as + an simple check against passing an arbitrary memory pointer. Here is a + typical call of pcre2_pattern_info(), to obtain the length of the com- piled pattern: int rc; @@ -2027,22 +1982,22 @@ INFORMATION ABOUT A COMPILED PATTERN PCRE2_INFO_EXTRAOPTIONS Return copies of the pattern's options. The third argument should point - to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the - options that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOP- - TIONS returns the compile options as modified by any top-level (*XXX) - option settings such as (*UTF) at the start of the pattern itself. - PCRE2_INFO_EXTRAOPTIONS returns the extra options that were set in the - compile context by calling the pcre2_set_compile_extra_options() func- + to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the + options that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOP- + TIONS returns the compile options as modified by any top-level (*XXX) + option settings such as (*UTF) at the start of the pattern itself. + PCRE2_INFO_EXTRAOPTIONS returns the extra options that were set in the + compile context by calling the pcre2_set_compile_extra_options() func- tion. - For example, if the pattern /(*UTF)abc/ is compiled with the - PCRE2_EXTENDED option, the result for PCRE2_INFO_ALLOPTIONS is - PCRE2_EXTENDED and PCRE2_UTF. Option settings such as (?i) that can - change within a pattern do not affect the result of PCRE2_INFO_ALLOP- + For example, if the pattern /(*UTF)abc/ is compiled with the + PCRE2_EXTENDED option, the result for PCRE2_INFO_ALLOPTIONS is + PCRE2_EXTENDED and PCRE2_UTF. Option settings such as (?i) that can + change within a pattern do not affect the result of PCRE2_INFO_ALLOP- TIONS, even if they appear right at the start of the pattern. (This was different in some earlier releases.) - A pattern compiled without PCRE2_ANCHORED is automatically anchored by + A pattern compiled without PCRE2_ANCHORED is automatically anchored by PCRE2 if the first significant item in every top-level branch is one of the following: @@ -2051,104 +2006,104 @@ INFORMATION ABOUT A COMPILED PATTERN \G always .* sometimes - see below - When .* is the first significant item, anchoring is possible only when + When .* is the first significant item, anchoring is possible only when all the following are true: .* is not in an atomic group - .* is not in a capture group that is the subject + .* is not in a capturing group that is the subject of a backreference PCRE2_DOTALL is in force for .* Neither (*PRUNE) nor (*SKIP) appears in the pattern PCRE2_NO_DOTSTAR_ANCHOR is not set - For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in + For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in the options returned for PCRE2_INFO_ALLOPTIONS. PCRE2_INFO_BACKREFMAX - Return the number of the highest backreference in the pattern. The - third argument should point to an uint32_t variable. Named capture - groups acquire numbers as well as names, and these count towards the - highest backreference. Backreferences such as \4 or \g{12} match the - captured characters of the given group, but in addition, the check that - a capture group is set in a conditional group such as (?(3)a|b) is also - a backreference. Zero is returned if there are no backreferences. + Return the number of the highest backreference in the pattern. The + third argument should point to an uint32_t variable. Named subpatterns + acquire numbers as well as names, and these count towards the highest + backreference. Backreferences such as \4 or \g{12} match the captured + characters of the given group, but in addition, the check that a cap- + turing group is set in a conditional subpattern such as (?(3)a|b) is + also a backreference. Zero is returned if there are no backreferences. PCRE2_INFO_BSR - The output is a uint32_t integer whose value indicates what character - sequences the \R escape sequence matches. A value of PCRE2_BSR_UNICODE - means that \R matches any Unicode line ending sequence; a value of + The output is a uint32_t integer whose value indicates what character + sequences the \R escape sequence matches. A value of PCRE2_BSR_UNICODE + means that \R matches any Unicode line ending sequence; a value of PCRE2_BSR_ANYCRLF means that \R matches only CR, LF, or CRLF. PCRE2_INFO_CAPTURECOUNT - Return the highest capture group number in the pattern. In patterns - where (?| is not used, this is also the total number of capture groups. - The third argument should point to an uint32_t variable. + Return the highest capturing subpattern number in the pattern. In pat- + terns where (?| is not used, this is also the total number of capturing + subpatterns. The third argument should point to an uint32_t variable. PCRE2_INFO_DEPTHLIMIT - If the pattern set a backtracking depth limit by including an item of - the form (*LIMIT_DEPTH=nnnn) at the start, the value is returned. The + If the pattern set a backtracking depth limit by including an item of + the form (*LIMIT_DEPTH=nnnn) at the start, the value is returned. The third argument should point to a uint32_t integer. If no such value has - been set, the call to pcre2_pattern_info() returns the error + been set, the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET. Note that this limit will only be used during match- - ing if it is less than the limit set or defaulted by the caller of the + ing if it is less than the limit set or defaulted by the caller of the match function. PCRE2_INFO_FIRSTBITMAP - In the absence of a single first code unit for a non-anchored pattern, - pcre2_compile() may construct a 256-bit table that defines a fixed set - of values for the first code unit in any match. For example, a pattern - that starts with [abc] results in a table with three bits set. When - code unit values greater than 255 are supported, the flag bit for 255 - means "any code unit of value 255 or above". If such a table was con- - structed, a pointer to it is returned. Otherwise NULL is returned. The + In the absence of a single first code unit for a non-anchored pattern, + pcre2_compile() may construct a 256-bit table that defines a fixed set + of values for the first code unit in any match. For example, a pattern + that starts with [abc] results in a table with three bits set. When + code unit values greater than 255 are supported, the flag bit for 255 + means "any code unit of value 255 or above". If such a table was con- + structed, a pointer to it is returned. Otherwise NULL is returned. The third argument should point to a const uint8_t * variable. PCRE2_INFO_FIRSTCODETYPE Return information about the first code unit of any matched string, for - a non-anchored pattern. The third argument should point to an uint32_t - variable. If there is a fixed first value, for example, the letter "c" - from a pattern such as (cat|cow|coyote), 1 is returned, and the value - can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed - first value, but it is known that a match can occur only at the start - of the subject or following a newline in the subject, 2 is returned. + a non-anchored pattern. The third argument should point to an uint32_t + variable. If there is a fixed first value, for example, the letter "c" + from a pattern such as (cat|cow|coyote), 1 is returned, and the value + can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed + first value, but it is known that a match can occur only at the start + of the subject or following a newline in the subject, 2 is returned. Otherwise, and for anchored patterns, 0 is returned. PCRE2_INFO_FIRSTCODEUNIT - Return the value of the first code unit of any matched string for a - pattern where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0. - The third argument should point to an uint32_t variable. In the 8-bit - library, the value is always less than 256. In the 16-bit library the - value can be up to 0xffff. In the 32-bit library in UTF-32 mode the + Return the value of the first code unit of any matched string for a + pattern where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0. + The third argument should point to an uint32_t variable. In the 8-bit + library, the value is always less than 256. In the 16-bit library the + value can be up to 0xffff. In the 32-bit library in UTF-32 mode the value can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32 mode. PCRE2_INFO_FRAMESIZE Return the size (in bytes) of the data frames that are used to remember - backtracking positions when the pattern is processed by pcre2_match() - without the use of JIT. The third argument should point to a size_t + backtracking positions when the pattern is processed by pcre2_match() + without the use of JIT. The third argument should point to a size_t variable. The frame size depends on the number of capturing parentheses - in the pattern. Each additional capture group adds two PCRE2_SIZE vari- - ables. + in the pattern. Each additional capturing group adds two PCRE2_SIZE + variables. PCRE2_INFO_HASBACKSLASHC - Return 1 if the pattern contains any instances of \C, otherwise 0. The + Return 1 if the pattern contains any instances of \C, otherwise 0. The third argument should point to an uint32_t variable. PCRE2_INFO_HASCRORLF - Return 1 if the pattern contains any explicit matches for CR or LF + Return 1 if the pattern contains any explicit matches for CR or LF characters, otherwise 0. The third argument should point to an uint32_t - variable. An explicit match is either a literal CR or LF character, or - \r or \n or one of the equivalent hexadecimal or octal escape + variable. An explicit match is either a literal CR or LF character, or + \r or \n or one of the equivalent hexadecimal or octal escape sequences. PCRE2_INFO_HEAPLIMIT @@ -2156,81 +2111,81 @@ INFORMATION ABOUT A COMPILED PATTERN If the pattern set a heap memory limit by including an item of the form (*LIMIT_HEAP=nnnn) at the start, the value is returned. The third argu- ment should point to a uint32_t integer. If no such value has been set, - the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET. - Note that this limit will only be used during matching if it is less + the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET. + Note that this limit will only be used during matching if it is less than the limit set or defaulted by the caller of the match function. PCRE2_INFO_JCHANGED - Return 1 if the (?J) or (?-J) option setting is used in the pattern, - otherwise 0. The third argument should point to an uint32_t variable. - (?J) and (?-J) set and unset the local PCRE2_DUPNAMES option, respec- + Return 1 if the (?J) or (?-J) option setting is used in the pattern, + otherwise 0. The third argument should point to an uint32_t variable. + (?J) and (?-J) set and unset the local PCRE2_DUPNAMES option, respec- tively. PCRE2_INFO_JITSIZE - If the compiled pattern was successfully processed by pcre2_jit_com- - pile(), return the size of the JIT compiled code, otherwise return + If the compiled pattern was successfully processed by pcre2_jit_com- + pile(), return the size of the JIT compiled code, otherwise return zero. The third argument should point to a size_t variable. PCRE2_INFO_LASTCODETYPE - Returns 1 if there is a rightmost literal code unit that must exist in - any matched string, other than at its start. The third argument should - point to an uint32_t variable. If there is no such value, 0 is - returned. When 1 is returned, the code unit value itself can be - retrieved using PCRE2_INFO_LASTCODEUNIT. For anchored patterns, a last - literal value is recorded only if it follows something of variable - length. For example, for the pattern /^a\d+z\d+/ the returned value is - 1 (with "z" returned from PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ + Returns 1 if there is a rightmost literal code unit that must exist in + any matched string, other than at its start. The third argument should + point to an uint32_t variable. If there is no such value, 0 is + returned. When 1 is returned, the code unit value itself can be + retrieved using PCRE2_INFO_LASTCODEUNIT. For anchored patterns, a last + literal value is recorded only if it follows something of variable + length. For example, for the pattern /^a\d+z\d+/ the returned value is + 1 (with "z" returned from PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is 0. PCRE2_INFO_LASTCODEUNIT - Return the value of the rightmost literal code unit that must exist in - any matched string, other than at its start, for a pattern where + Return the value of the rightmost literal code unit that must exist in + any matched string, other than at its start, for a pattern where PCRE2_INFO_LASTCODETYPE returns 1. Otherwise, return 0. The third argu- ment should point to an uint32_t variable. PCRE2_INFO_MATCHEMPTY - Return 1 if the pattern might match an empty string, otherwise 0. The - third argument should point to an uint32_t variable. When a pattern + Return 1 if the pattern might match an empty string, otherwise 0. The + third argument should point to an uint32_t variable. When a pattern contains recursive subroutine calls it is not always possible to deter- - mine whether or not it can match an empty string. PCRE2 takes a cau- + mine whether or not it can match an empty string. PCRE2 takes a cau- tious approach and returns 1 in such cases. PCRE2_INFO_MATCHLIMIT - If the pattern set a match limit by including an item of the form - (*LIMIT_MATCH=nnnn) at the start, the value is returned. The third - argument should point to a uint32_t integer. If no such value has been - set, the call to pcre2_pattern_info() returns the error + If the pattern set a match limit by including an item of the form + (*LIMIT_MATCH=nnnn) at the start, the value is returned. The third + argument should point to a uint32_t integer. If no such value has been + set, the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET. Note that this limit will only be used during match- - ing if it is less than the limit set or defaulted by the caller of the + ing if it is less than the limit set or defaulted by the caller of the match function. PCRE2_INFO_MAXLOOKBEHIND Return the number of characters (not code units) in the longest lookbe- - hind assertion in the pattern. The third argument should point to a - uint32_t integer. This information is useful when doing multi-segment - matching using the partial matching facilities. Note that the simple + hind assertion in the pattern. The third argument should point to a + uint32_t integer. This information is useful when doing multi-segment + matching using the partial matching facilities. Note that the simple assertions \b and \B require a one-character lookbehind. \A also regis- - ters a one-character lookbehind, though it does not actually inspect - the previous character. This is to ensure that at least one character - from the old segment is retained when a new segment is processed. Oth- - erwise, if there are no lookbehinds in the pattern, \A might match + ters a one-character lookbehind, though it does not actually inspect + the previous character. This is to ensure that at least one character + from the old segment is retained when a new segment is processed. Oth- + erwise, if there are no lookbehinds in the pattern, \A might match incorrectly at the start of a second or subsequent segment. PCRE2_INFO_MINLENGTH - If a minimum length for matching subject strings was computed, its - value is returned. Otherwise the returned value is 0. The value is a - number of characters, which in UTF mode may be different from the num- - ber of code units. The third argument should point to an uint32_t - variable. The value is a lower bound to the length of any matching - string. There may not be any strings of that length that do actually + If a minimum length for matching subject strings was computed, its + value is returned. Otherwise the returned value is 0. The value is a + number of characters, which in UTF mode may be different from the num- + ber of code units. The third argument should point to an uint32_t + variable. The value is a lower bound to the length of any matching + string. There may not be any strings of that length that do actually match, but every string that does match is at least that long. PCRE2_INFO_NAMECOUNT @@ -2238,41 +2193,40 @@ INFORMATION ABOUT A COMPILED PATTERN PCRE2_INFO_NAMETABLE PCRE2 supports the use of named as well as numbered capturing parenthe- - ses. The names are just an additional way of identifying the parenthe- + ses. The names are just an additional way of identifying the parenthe- ses, which still acquire numbers. Several convenience functions such as - pcre2_substring_get_byname() are provided for extracting captured sub- - strings by name. It is also possible to extract the data directly, by - first converting the name to a number in order to access the correct - pointers in the output vector (described with pcre2_match() below). To - do the conversion, you need to use the name-to-number map, which is + pcre2_substring_get_byname() are provided for extracting captured sub- + strings by name. It is also possible to extract the data directly, by + first converting the name to a number in order to access the correct + pointers in the output vector (described with pcre2_match() below). To + do the conversion, you need to use the name-to-number map, which is described by these three values. - The map consists of a number of fixed-size entries. PCRE2_INFO_NAME- - COUNT gives the number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives - the size of each entry in code units; both of these return a uint32_t + The map consists of a number of fixed-size entries. PCRE2_INFO_NAME- + COUNT gives the number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives + the size of each entry in code units; both of these return a uint32_t value. The entry size depends on the length of the longest name. PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the table. - This is a PCRE2_SPTR pointer to a block of code units. In the 8-bit - library, the first two bytes of each entry are the number of the cap- + This is a PCRE2_SPTR pointer to a block of code units. In the 8-bit + library, the first two bytes of each entry are the number of the cap- turing parenthesis, most significant byte first. In the 16-bit library, - the pointer points to 16-bit code units, the first of which contains - the parenthesis number. In the 32-bit library, the pointer points to - 32-bit code units, the first of which contains the parenthesis number. + the pointer points to 16-bit code units, the first of which contains + the parenthesis number. In the 32-bit library, the pointer points to + 32-bit code units, the first of which contains the parenthesis number. The rest of the entry is the corresponding name, zero terminated. - The names are in alphabetical order. If (?| is used to create multiple - capture groups with the same number, as described in the section on - duplicate group numbers in the pcre2pattern page, the groups may be - given the same name, but there is only one entry in the table. Differ- - ent names for groups of the same number are not permitted. + The names are in alphabetical order. If (?| is used to create multiple + groups with the same number, as described in the section on duplicate + subpattern numbers in the pcre2pattern page, the groups may be given + the same name, but there is only one entry in the table. Different + names for groups of the same number are not permitted. - Duplicate names for capture groups with different numbers are permit- - ted, but only if PCRE2_DUPNAMES is set. They appear in the table in the - order in which they were found in the pattern. In the absence of (?| - this is the order of increasing number; when (?| is used this is not - necessarily the case because later capture groups may have lower num- - bers. + Duplicate names for subpatterns with different numbers are permitted, + but only if PCRE2_DUPNAMES is set. They appear in the table in the + order in which they were found in the pattern. In the absence of (?| + this is the order of increasing number; when (?| is used this is not + necessarily the case because later subpatterns may have lower numbers. As a simple example of the name/number table, consider the following pattern after compilation by the 8-bit library (assume PCRE2_EXTENDED @@ -2281,7 +2235,7 @@ INFORMATION ABOUT A COMPILED PATTERN (?<date> (?<year>(\d\d)?\d\d) - (?<month>\d\d) - (?<day>\d\d) ) - There are four named capture groups, so the table has four entries, and + There are four named subpatterns, so the table has four entries, and each entry in the table is eight bytes long. The table is as follows, with non-printing bytes shows in hexadecimal, and undefined bytes shown as ??: @@ -2291,7 +2245,7 @@ INFORMATION ABOUT A COMPILED PATTERN 00 04 m o n t h 00 00 02 y e a r 00 ?? - When writing code to extract data from named capture groups using the + When writing code to extract data from named subpatterns using the name-to-number map, remember that the length of the entries is likely to be different for each compiled pattern. @@ -2410,16 +2364,13 @@ THE MATCH DATA BLOCK When one of the matching functions is called, pointers to the compiled pattern and the subject string are set in the match data block so that - they can be referenced by the extraction functions after a successful - match. After running a match, you must not free a compiled pattern or a - subject string until after all operations on the match data block (for - that match) have taken place, unless, in the case of the subject - string, you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is - described in the section entitled "Option bits for pcre2_match()" - below. + they can be referenced by the extraction functions. After running a + match, you must not free a compiled pattern or a subject string until + after all operations on the match data block (for that match) have + taken place. - When a match data block itself is no longer needed, it should be freed - by calling pcre2_match_data_free(). If this function is called with a + When a match data block itself is no longer needed, it should be freed + by calling pcre2_match_data_free(). If this function is called with a NULL argument, it returns immediately, without doing anything. @@ -2430,15 +2381,15 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION uint32_t options, pcre2_match_data *match_data, pcre2_match_context *mcontext); - The function pcre2_match() is called to match a subject string against - a compiled pattern, which is passed in the code argument. You can call + The function pcre2_match() is called to match a subject string against + a compiled pattern, which is passed in the code argument. You can call pcre2_match() with the same code argument as many times as you like, in - order to find multiple matches in the subject string or to match dif- + order to find multiple matches in the subject string or to match dif- ferent subject strings with the same pattern. - This function is the main matching facility of the library, and it - operates in a Perl-like manner. For specialist use there is also an - alternative matching function, which is described below in the section + This function is the main matching facility of the library, and it + operates in a Perl-like manner. For specialist use there is also an + alternative matching function, which is described below in the section about the pcre2_dfa_match() function. Here is an example of a simple call to pcre2_match(): @@ -2453,74 +2404,73 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION md, /* the match data block */ NULL); /* a match context; NULL means use defaults */ - If the subject string is zero-terminated, the length can be given as + If the subject string is zero-terminated, the length can be given as PCRE2_ZERO_TERMINATED. A match context must be provided if certain less common matching parameters are to be changed. For details, see the sec- tion on the match context above. The string to be matched by pcre2_match() - The subject string is passed to pcre2_match() as a pointer in subject, - a length in length, and a starting offset in startoffset. The length - and offset are in code units, not characters. That is, they are in - bytes for the 8-bit library, 16-bit code units for the 16-bit library, - and 32-bit code units for the 32-bit library, whether or not UTF pro- + The subject string is passed to pcre2_match() as a pointer in subject, + a length in length, and a starting offset in startoffset. The length + and offset are in code units, not characters. That is, they are in + bytes for the 8-bit library, 16-bit code units for the 16-bit library, + and 32-bit code units for the 32-bit library, whether or not UTF pro- cessing is enabled. If startoffset is greater than the length of the subject, pcre2_match() - returns PCRE2_ERROR_BADOFFSET. When the starting offset is zero, the - search for a match starts at the beginning of the subject, and this is + returns PCRE2_ERROR_BADOFFSET. When the starting offset is zero, the + search for a match starts at the beginning of the subject, and this is by far the most common case. In UTF-8 or UTF-16 mode, the starting off- - set must point to the start of a character, or to the end of the sub- - ject (in UTF-32 mode, one code unit equals one character, so all off- - sets are valid). Like the pattern string, the subject may contain + set must point to the start of a character, or to the end of the sub- + ject (in UTF-32 mode, one code unit equals one character, so all off- + sets are valid). Like the pattern string, the subject may contain binary zeros. - A non-zero starting offset is useful when searching for another match - in the same subject by calling pcre2_match() again after a previous - success. Setting startoffset differs from passing over a shortened - string and setting PCRE2_NOTBOL in the case of a pattern that begins + A non-zero starting offset is useful when searching for another match + in the same subject by calling pcre2_match() again after a previous + success. Setting startoffset differs from passing over a shortened + string and setting PCRE2_NOTBOL in the case of a pattern that begins with any kind of lookbehind. For example, consider the pattern \Biss\B - which finds occurrences of "iss" in the middle of words. (\B matches - only if the current position in the subject is not a word boundary.) + which finds occurrences of "iss" in the middle of words. (\B matches + only if the current position in the subject is not a word boundary.) When applied to the string "Mississipi" the first call to pcre2_match() - finds the first occurrence. If pcre2_match() is called again with just - the remainder of the subject, namely "issipi", it does not match, + finds the first occurrence. If pcre2_match() is called again with just + the remainder of the subject, namely "issipi", it does not match, because \B is always false at the start of the subject, which is deemed - to be a word boundary. However, if pcre2_match() is passed the entire + to be a word boundary. However, if pcre2_match() is passed the entire string again, but with startoffset set to 4, it finds the second occur- - rence of "iss" because it is able to look behind the starting point to + rence of "iss" because it is able to look behind the starting point to discover that it is preceded by a letter. - Finding all the matches in a subject is tricky when the pattern can + Finding all the matches in a subject is tricky when the pattern can match an empty string. It is possible to emulate Perl's /g behaviour by - first trying the match again at the same offset, with the - PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED options, and then if that - fails, advancing the starting offset and trying an ordinary match - again. There is some code that demonstrates how to do this in the - pcre2demo sample program. In the most general case, you have to check - to see if the newline convention recognizes CRLF as a newline, and if - so, and the current character is CR followed by LF, advance the start- + first trying the match again at the same offset, with the + PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED options, and then if that + fails, advancing the starting offset and trying an ordinary match + again. There is some code that demonstrates how to do this in the + pcre2demo sample program. In the most general case, you have to check + to see if the newline convention recognizes CRLF as a newline, and if + so, and the current character is CR followed by LF, advance the start- ing offset by two characters instead of one. If a non-zero starting offset is passed when the pattern is anchored, a single attempt to match at the given offset is made. This can only suc- - ceed if the pattern does not require the match to be at the start of - the subject. In other words, the anchoring must be the result of set- - ting the PCRE2_ANCHORED option or the use of .* with PCRE2_DOTALL, not + ceed if the pattern does not require the match to be at the start of + the subject. In other words, the anchoring must be the result of set- + ting the PCRE2_ANCHORED option or the use of .* with PCRE2_DOTALL, not by starting the pattern with ^ or \A. Option bits for pcre2_match() The unused bits of the options argument for pcre2_match() must be zero. - The only bits that may be set are PCRE2_ANCHORED, - PCRE2_COPY_MATCHED_SUBJECT, PCRE2_ENDANCHORED, PCRE2_NOTBOL, - PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_JIT, - PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. Their - action is described below. + The only bits that may be set are PCRE2_ANCHORED, PCRE2_ENDANCHORED, + PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, + PCRE2_NO_JIT, PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PAR- + TIAL_SOFT. Their action is described below. Setting PCRE2_ANCHORED or PCRE2_ENDANCHORED at match time is not sup- ported by the just-in-time (JIT) compiler. If it is set, JIT matching @@ -2536,122 +2486,105 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION unachored at matching time. Note that setting the option at match time disables JIT matching. - PCRE2_COPY_MATCHED_SUBJECT - - By default, a pointer to the subject is remembered in the match data - block so that, after a successful match, it can be referenced by the - substring extraction functions. This means that the subject's memory - must not be freed until all such operations are complete. For some - applications where the lifetime of the subject string is not guaran- - teed, it may be necessary to make a copy of the subject string, but it - is wasteful to do this unless the match is successful. After a success- - ful match, if PCRE2_COPY_MATCHED_SUBJECT is set, the subject is copied - and the new pointer is remembered in the match data block instead of - the original subject pointer. The memory allocator that was used for - the match block itself is used. The copy is automatically freed when - pcre2_match_data_free() is called to free the match data block. It is - also automatically freed if the match data block is re-used for another - match operation. - PCRE2_ENDANCHORED - If the PCRE2_ENDANCHORED option is set, any string that pcre2_match() - matches must be right at the end of the subject string. Note that set- + If the PCRE2_ENDANCHORED option is set, any string that pcre2_match() + matches must be right at the end of the subject string. Note that set- ting the option at match time disables JIT matching. PCRE2_NOTBOL This option specifies that first character of the subject string is not - the beginning of a line, so the circumflex metacharacter should not - match before it. Setting this without having set PCRE2_MULTILINE at + the beginning of a line, so the circumflex metacharacter should not + match before it. Setting this without having set PCRE2_MULTILINE at compile time causes circumflex never to match. This option affects only the behaviour of the circumflex metacharacter. It does not affect \A. PCRE2_NOTEOL This option specifies that the end of the subject string is not the end - of a line, so the dollar metacharacter should not match it nor (except - in multiline mode) a newline immediately before it. Setting this with- - out having set PCRE2_MULTILINE at compile time causes dollar never to + of a line, so the dollar metacharacter should not match it nor (except + in multiline mode) a newline immediately before it. Setting this with- + out having set PCRE2_MULTILINE at compile time causes dollar never to match. This option affects only the behaviour of the dollar metacharac- ter. It does not affect \Z or \z. PCRE2_NOTEMPTY An empty string is not considered to be a valid match if this option is - set. If there are alternatives in the pattern, they are tried. If all - the alternatives match the empty string, the entire match fails. For + set. If there are alternatives in the pattern, they are tried. If all + the alternatives match the empty string, the entire match fails. For example, if the pattern a?b? - is applied to a string not beginning with "a" or "b", it matches an + is applied to a string not beginning with "a" or "b", it matches an empty string at the start of the subject. With PCRE2_NOTEMPTY set, this - match is not valid, so pcre2_match() searches further into the string + match is not valid, so pcre2_match() searches further into the string for occurrences of "a" or "b". PCRE2_NOTEMPTY_ATSTART - This is like PCRE2_NOTEMPTY, except that it locks out an empty string + This is like PCRE2_NOTEMPTY, except that it locks out an empty string match only at the first matching position, that is, at the start of the - subject plus the starting offset. An empty string match later in the - subject is permitted. If the pattern is anchored, such a match can + subject plus the starting offset. An empty string match later in the + subject is permitted. If the pattern is anchored, such a match can occur only if the pattern contains \K. PCRE2_NO_JIT - By default, if a pattern has been successfully processed by - pcre2_jit_compile(), JIT is automatically used when pcre2_match() is - called with options that JIT supports. Setting PCRE2_NO_JIT disables + By default, if a pattern has been successfully processed by + pcre2_jit_compile(), JIT is automatically used when pcre2_match() is + called with options that JIT supports. Setting PCRE2_NO_JIT disables the use of JIT; it forces matching to be done by the interpreter. PCRE2_NO_UTF_CHECK When PCRE2_UTF is set at compile time, the validity of the subject as a - UTF string is checked by default when pcre2_match() is subsequently - called. If a non-zero starting offset is given, the check is applied - only to that part of the subject that could be inspected during match- - ing, and there is a check that the starting offset points to the first - code unit of a character or to the end of the subject. If there are no - lookbehind assertions in the pattern, the check starts at the starting - offset. Otherwise, it starts at the length of the longest lookbehind + UTF string is checked by default when pcre2_match() is subsequently + called. If a non-zero starting offset is given, the check is applied + only to that part of the subject that could be inspected during match- + ing, and there is a check that the starting offset points to the first + code unit of a character or to the end of the subject. If there are no + lookbehind assertions in the pattern, the check starts at the starting + offset. Otherwise, it starts at the length of the longest lookbehind before the starting offset, or at the start of the subject if there are - not that many characters before the starting offset. Note that the + not that many characters before the starting offset. Note that the sequences \b and \B are one-character lookbehinds. The check is carried out before any other processing takes place, and a - negative error code is returned if the check fails. There are several - UTF error codes for each code unit width, corresponding to different - problems with the code unit sequence. There are discussions about the - validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the + negative error code is returned if the check fails. There are several + UTF error codes for each code unit width, corresponding to different + problems with the code unit sequence. There are discussions about the + validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the pcre2unicode page. - If you know that your subject is valid, and you want to skip these - checks for performance reasons, you can set the PCRE2_NO_UTF_CHECK - option when calling pcre2_match(). You might want to do this for the + If you know that your subject is valid, and you want to skip these + checks for performance reasons, you can set the PCRE2_NO_UTF_CHECK + option when calling pcre2_match(). You might want to do this for the second and subsequent calls to pcre2_match() if you are making repeated calls to find other matches in the same subject string. - Warning: When PCRE2_NO_UTF_CHECK is set, the effect of passing an - invalid string as a subject, or an invalid value of startoffset, is + Warning: When PCRE2_NO_UTF_CHECK is set, the effect of passing an + invalid string as a subject, or an invalid value of startoffset, is undefined. Your program may crash or loop indefinitely. PCRE2_PARTIAL_HARD PCRE2_PARTIAL_SOFT - These options turn on the partial matching feature. A partial match - occurs if the end of the subject string is reached successfully, but - there are not enough subject characters to complete the match. If this - happens when PCRE2_PARTIAL_SOFT (but not PCRE2_PARTIAL_HARD) is set, - matching continues by testing any remaining alternatives. Only if no - complete match can be found is PCRE2_ERROR_PARTIAL returned instead of - PCRE2_ERROR_NOMATCH. In other words, PCRE2_PARTIAL_SOFT specifies that - the caller is prepared to handle a partial match, but only if no com- + These options turn on the partial matching feature. A partial match + occurs if the end of the subject string is reached successfully, but + there are not enough subject characters to complete the match. If this + happens when PCRE2_PARTIAL_SOFT (but not PCRE2_PARTIAL_HARD) is set, + matching continues by testing any remaining alternatives. Only if no + complete match can be found is PCRE2_ERROR_PARTIAL returned instead of + PCRE2_ERROR_NOMATCH. In other words, PCRE2_PARTIAL_SOFT specifies that + the caller is prepared to handle a partial match, but only if no com- plete match can be found. - If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this - case, if a partial match is found, pcre2_match() immediately returns - PCRE2_ERROR_PARTIAL, without considering any other alternatives. In + If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this + case, if a partial match is found, pcre2_match() immediately returns + PCRE2_ERROR_PARTIAL, without considering any other alternatives. In other words, when PCRE2_PARTIAL_HARD is set, a partial match is consid- ered to be more important that an alternative complete match. @@ -2661,38 +2594,38 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION NEWLINE HANDLING WHEN MATCHING - When PCRE2 is built, a default newline convention is set; this is usu- - ally the standard convention for the operating system. The default can - be overridden in a compile context by calling pcre2_set_newline(). It - can also be overridden by starting a pattern string with, for example, - (*CRLF), as described in the section on newline conventions in the - pcre2pattern page. During matching, the newline choice affects the be- - haviour of the dot, circumflex, and dollar metacharacters. It may also - alter the way the match starting position is advanced after a match + When PCRE2 is built, a default newline convention is set; this is usu- + ally the standard convention for the operating system. The default can + be overridden in a compile context by calling pcre2_set_newline(). It + can also be overridden by starting a pattern string with, for example, + (*CRLF), as described in the section on newline conventions in the + pcre2pattern page. During matching, the newline choice affects the be- + haviour of the dot, circumflex, and dollar metacharacters. It may also + alter the way the match starting position is advanced after a match failure for an unanchored pattern. When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY is - set as the newline convention, and a match attempt for an unanchored + set as the newline convention, and a match attempt for an unanchored pattern fails when the current starting position is at a CRLF sequence, - and the pattern contains no explicit matches for CR or LF characters, - the match position is advanced by two characters instead of one, in + and the pattern contains no explicit matches for CR or LF characters, + the match position is advanced by two characters instead of one, in other words, to after the CRLF. The above rule is a compromise that makes the most common cases work as - expected. For example, if the pattern is .+A (and the PCRE2_DOTALL + expected. For example, if the pattern is .+A (and the PCRE2_DOTALL option is not set), it does not match the string "\r\nA" because, after - failing at the start, it skips both the CR and the LF before retrying. - However, the pattern [\r\n]A does match that string, because it con- + failing at the start, it skips both the CR and the LF before retrying. + However, the pattern [\r\n]A does match that string, because it con- tains an explicit CR or LF reference, and so advances only by one char- acter after the first failure. An explicit match for CR of LF is either a literal appearance of one of - those characters in the pattern, or one of the \r or \n or equivalent + those characters in the pattern, or one of the \r or \n or equivalent octal or hexadecimal escape sequences. Implicit matches such as [^X] do - not count, nor does \s, even though it includes CR and LF in the char- + not count, nor does \s, even though it includes CR and LF in the char- acters that it matches. - Notwithstanding the above, anomalous effects may still occur when CRLF + Notwithstanding the above, anomalous effects may still occur when CRLF is a valid newline sequence and explicit \r or \n escapes appear in the pattern. @@ -2703,82 +2636,82 @@ HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data); - In general, a pattern matches a certain portion of the subject, and in - addition, further substrings from the subject may be picked out by - parenthesized parts of the pattern. Following the usage in Jeffrey - Friedl's book, this is called "capturing" in what follows, and the - phrase "capture group" (Perl terminology) is used for a fragment of a - pattern that picks out a substring. PCRE2 supports several other kinds - of parenthesized group that do not cause substrings to be captured. The - pcre2_pattern_info() function can be used to find out how many capture - groups there are in a compiled pattern. - - You can use auxiliary functions for accessing captured substrings by + In general, a pattern matches a certain portion of the subject, and in + addition, further substrings from the subject may be picked out by + parenthesized parts of the pattern. Following the usage in Jeffrey + Friedl's book, this is called "capturing" in what follows, and the + phrase "capturing subpattern" or "capturing group" is used for a frag- + ment of a pattern that picks out a substring. PCRE2 supports several + other kinds of parenthesized subpattern that do not cause substrings to + be captured. The pcre2_pattern_info() function can be used to find out + how many capturing subpatterns there are in a compiled pattern. + + You can use auxiliary functions for accessing captured substrings by number or by name, as described in sections below. Alternatively, you can make direct use of the vector of PCRE2_SIZE val- - ues, called the ovector, which contains the offsets of captured - strings. It is part of the match data block. The function - pcre2_get_ovector_pointer() returns the address of the ovector, and + ues, called the ovector, which contains the offsets of captured + strings. It is part of the match data block. The function + pcre2_get_ovector_pointer() returns the address of the ovector, and pcre2_get_ovector_count() returns the number of pairs of values it con- tains. Within the ovector, the first in each pair of values is set to the off- set of the first code unit of a substring, and the second is set to the - offset of the first code unit after the end of a substring. These val- - ues are always code unit offsets, not character offsets. That is, they - are byte offsets in the 8-bit library, 16-bit offsets in the 16-bit + offset of the first code unit after the end of a substring. These val- + ues are always code unit offsets, not character offsets. That is, they + are byte offsets in the 8-bit library, 16-bit offsets in the 16-bit library, and 32-bit offsets in the 32-bit library. - After a partial match (error return PCRE2_ERROR_PARTIAL), only the - first pair of offsets (that is, ovector[0] and ovector[1]) are set. - They identify the part of the subject that was partially matched. See + After a partial match (error return PCRE2_ERROR_PARTIAL), only the + first pair of offsets (that is, ovector[0] and ovector[1]) are set. + They identify the part of the subject that was partially matched. See the pcre2partial documentation for details of partial matching. - After a fully successful match, the first pair of offsets identifies - the portion of the subject string that was matched by the entire pat- - tern. The next pair is used for the first captured substring, and so - on. The value returned by pcre2_match() is one more than the highest - numbered pair that has been set. For example, if two substrings have - been captured, the returned value is 3. If there are no captured sub- + After a fully successful match, the first pair of offsets identifies + the portion of the subject string that was matched by the entire pat- + tern. The next pair is used for the first captured substring, and so + on. The value returned by pcre2_match() is one more than the highest + numbered pair that has been set. For example, if two substrings have + been captured, the returned value is 3. If there are no captured sub- strings, the return value from a successful match is 1, indicating that just the first pair of offsets has been set. - If a pattern uses the \K escape sequence within a positive assertion, + If a pattern uses the \K escape sequence within a positive assertion, the reported start of a successful match can be greater than the end of - the match. For example, if the pattern (?=ab\K) is matched against + the match. For example, if the pattern (?=ab\K) is matched against "ab", the start and end offset values for the match are 2 and 0. - If a capture group is matched repeatedly within a single match opera- - tion, it is the last portion of the subject that it matched that is - returned. + If a capturing subpattern group is matched repeatedly within a single + match operation, it is the last portion of the subject that it matched + that is returned. If the ovector is too small to hold all the captured substring offsets, - as much as possible is filled in, and the function returns a value of - zero. If captured substrings are not of interest, pcre2_match() may be + as much as possible is filled in, and the function returns a value of + zero. If captured substrings are not of interest, pcre2_match() may be called with a match data block whose ovector is of minimum length (that is, one pair). - It is possible for capture group number n+1 to match some part of the - subject when group n has not been used at all. For example, if the - string "abc" is matched against the pattern (a|(z))(bc) the return from - the function is 4, and groups 1 and 3 are matched, but 2 is not. When - this happens, both values in the offset pairs corresponding to unused - groups are set to PCRE2_UNSET. - - Offset values that correspond to unused groups at the end of the - expression are also set to PCRE2_UNSET. For example, if the string - "abc" is matched against the pattern (abc)(x(yz)?)? groups 2 and 3 are - not matched. The return from the function is 2, because the highest - used capture group number is 1. The offsets for for the second and - third capture groupss (assuming the vector is large enough, of course) - are set to PCRE2_UNSET. + It is possible for capturing subpattern number n+1 to match some part + of the subject when subpattern n has not been used at all. For example, + if the string "abc" is matched against the pattern (a|(z))(bc) the + return from the function is 4, and subpatterns 1 and 3 are matched, but + 2 is not. When this happens, both values in the offset pairs corre- + sponding to unused subpatterns are set to PCRE2_UNSET. + + Offset values that correspond to unused subpatterns at the end of the + expression are also set to PCRE2_UNSET. For example, if the string + "abc" is matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 + are not matched. The return from the function is 2, because the high- + est used capturing subpattern number is 1. The offsets for for the sec- + ond and third capturing subpatterns (assuming the vector is large + enough, of course) are set to PCRE2_UNSET. Elements in the ovector that do not correspond to capturing parentheses in the pattern are never changed. That is, if a pattern contains n cap- turing parentheses, no more than ovector[0] to ovector[2n+1] are set by - pcre2_match(). The other elements retain whatever values they previ- - ously had. After a failed match attempt, the contents of the ovector + pcre2_match(). The other elements retain whatever values they previ- + ously had. After a failed match attempt, the contents of the ovector are unchanged. @@ -2788,69 +2721,69 @@ OTHER INFORMATION ABOUT A MATCH PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data); - As well as the offsets in the ovector, other information about a match - is retained in the match data block and can be retrieved by the above - functions in appropriate circumstances. If they are called at other + As well as the offsets in the ovector, other information about a match + is retained in the match data block and can be retrieved by the above + functions in appropriate circumstances. If they are called at other times, the result is undefined. - After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a - failure to match (PCRE2_ERROR_NOMATCH), a mark name may be available. - The function pcre2_get_mark() can be called to access this name, which - can be specified in the pattern by any of the backtracking control - verbs, not just (*MARK). The same function applies to all the verbs. It + After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a + failure to match (PCRE2_ERROR_NOMATCH), a (*MARK), (*PRUNE), or (*THEN) + name may be available. The function pcre2_get_mark() can be called to + access this name. The same function applies to all three verbs. It returns a pointer to the zero-terminated name, which is within the com- piled pattern. If no name is available, NULL is returned. The length of the name (excluding the terminating zero) is stored in the code unit that precedes the name. You should use this length instead of relying on the terminating zero if the name might contain a binary zero. - After a successful match, the name that is returned is the last mark - name encountered on the matching path through the pattern. Instances of - backtracking verbs without names do not count. Thus, for example, if - the matching path contains (*MARK:A)(*PRUNE), the name "A" is returned. - After a "no match" or a partial match, the last encountered name is - returned. For example, consider this pattern: + After a successful match, the name that is returned is the last + (*MARK), (*PRUNE), or (*THEN) name encountered on the matching path + through the pattern. Instances of (*PRUNE) and (*THEN) without names + are ignored. Thus, for example, if the matching path contains + (*MARK:A)(*PRUNE), the name "A" is returned. After a "no match" or a + partial match, the last encountered name is returned. For example, + consider this pattern: ^(*MARK:A)((*MARK:B)a|b)c - When it matches "bc", the returned name is A. The B mark is "seen" in - the first branch of the group, but it is not on the matching path. On - the other hand, when this pattern fails to match "bx", the returned + When it matches "bc", the returned name is A. The B mark is "seen" in + the first branch of the group, but it is not on the matching path. On + the other hand, when this pattern fails to match "bx", the returned name is B. - Warning: By default, certain start-of-match optimizations are used to - give a fast "no match" result in some situations. For example, if the - anchoring is removed from the pattern above, there is an initial check - for the presence of "c" in the subject before running the matching + Warning: By default, certain start-of-match optimizations are used to + give a fast "no match" result in some situations. For example, if the + anchoring is removed from the pattern above, there is an initial check + for the presence of "c" in the subject before running the matching engine. This check fails for "bx", causing a match failure without see- ing any marks. You can disable the start-of-match optimizations by set- - ting the PCRE2_NO_START_OPTIMIZE option for pcre2_compile() or by - starting the pattern with (*NO_START_OPT). + ting the PCRE2_NO_START_OPTIMIZE option for pcre2_compile() or starting + the pattern with (*NO_START_OPT). - After a successful match, a partial match, or one of the invalid UTF - errors (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can + After a successful match, a partial match, or one of the invalid UTF + errors (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can be called. After a successful or partial match it returns the code unit - offset of the character at which the match started. For a non-partial - match, this can be different to the value of ovector[0] if the pattern - contains the \K escape sequence. After a partial match, however, this - value is always the same as ovector[0] because \K does not affect the + offset of the character at which the match started. For a non-partial + match, this can be different to the value of ovector[0] if the pattern + contains the \K escape sequence. After a partial match, however, this + value is always the same as ovector[0] because \K does not affect the result of a partial match. - After a UTF check failure, pcre2_get_startchar() can be used to obtain + After a UTF check failure, pcre2_get_startchar() can be used to obtain the code unit offset of the invalid UTF character. Details are given in the pcre2unicode page. ERROR RETURNS FROM pcre2_match() - If pcre2_match() fails, it returns a negative number. This can be con- - verted to a text string by calling the pcre2_get_error_message() func- - tion (see "Obtaining a textual error message" below). Negative error - codes are also returned by other functions, and are documented with - them. The codes are given names in the header file. If UTF checking is + If pcre2_match() fails, it returns a negative number. This can be con- + verted to a text string by calling the pcre2_get_error_message() func- + tion (see "Obtaining a textual error message" below). Negative error + codes are also returned by other functions, and are documented with + them. The codes are given names in the header file. If UTF checking is in force and an invalid UTF subject string is detected, one of a number - of UTF-specific negative error codes is returned. Details are given in - the pcre2unicode page. The following are the other errors that may be + of UTF-specific negative error codes is returned. Details are given in + the pcre2unicode page. The following are the other errors that may be returned by pcre2_match(): PCRE2_ERROR_NOMATCH @@ -2859,20 +2792,20 @@ ERROR RETURNS FROM pcre2_match() PCRE2_ERROR_PARTIAL - The subject string did not match, but it did match partially. See the + The subject string did not match, but it did match partially. See the pcre2partial documentation for details of partial matching. PCRE2_ERROR_BADMAGIC PCRE2 stores a 4-byte "magic number" at the start of the compiled code, - to catch the case when it is passed a junk pointer. This is the error + to catch the case when it is passed a junk pointer. This is the error that is returned when the magic number is not present. PCRE2_ERROR_BADMODE - This error is given when a compiled pattern is passed to a function in - a library of a different code unit width, for example, a pattern com- - piled by the 8-bit library is passed to a 16-bit or 32-bit library + This error is given when a compiled pattern is passed to a function in + a library of a different code unit width, for example, a pattern com- + piled by the 8-bit library is passed to a 16-bit or 32-bit library function. PCRE2_ERROR_BADOFFSET @@ -2886,15 +2819,15 @@ ERROR RETURNS FROM pcre2_match() PCRE2_ERROR_BADUTFOFFSET The UTF code unit sequence that was passed as a subject was checked and - found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but the - value of startoffset did not point to the beginning of a UTF character + found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but the + value of startoffset did not point to the beginning of a UTF character or the end of the subject. PCRE2_ERROR_CALLOUT - This error is never generated by pcre2_match() itself. It is provided - for use by callout functions that want to cause pcre2_match() or - pcre2_callout_enumerate() to return a distinctive error code. See the + This error is never generated by pcre2_match() itself. It is provided + for use by callout functions that want to cause pcre2_match() or + pcre2_callout_enumerate() to return a distinctive error code. See the pcre2callout documentation for details. PCRE2_ERROR_DEPTHLIMIT @@ -2907,14 +2840,14 @@ ERROR RETURNS FROM pcre2_match() PCRE2_ERROR_INTERNAL - An unexpected internal error has occurred. This error could be caused + An unexpected internal error has occurred. This error could be caused by a bug in PCRE2 or by overwriting of the compiled pattern. PCRE2_ERROR_JIT_STACKLIMIT - This error is returned when a pattern that was successfully studied - using JIT is being matched, but the memory available for the just-in- - time processing stack is not large enough. See the pcre2jit documenta- + This error is returned when a pattern that was successfully studied + using JIT is being matched, but the memory available for the just-in- + time processing stack is not large enough. See the pcre2jit documenta- tion for more details. PCRE2_ERROR_MATCHLIMIT @@ -2923,12 +2856,11 @@ ERROR RETURNS FROM pcre2_match() PCRE2_ERROR_NOMEMORY - If a pattern contains many nested backtracking points, heap memory is - used to remember them. This error is given when the memory allocation - function (default or custom) fails. Note that a different error, - PCRE2_ERROR_HEAPLIMIT, is given if the amount of memory needed exceeds - the heap limit. PCRE2_ERROR_NOMEMORY is also returned if - PCRE2_COPY_MATCHED_SUBJECT is set and memory allocation fails. + If a pattern contains many nested backtracking points, heap memory is + used to remember them. This error is given when the memory allocation + function (default or custom) fails. Note that a different error, + PCRE2_ERROR_HEAPLIMIT, is given if the amount of memory needed exceeds + the heap limit. PCRE2_ERROR_NULL @@ -2938,11 +2870,11 @@ ERROR RETURNS FROM pcre2_match() This error is returned when pcre2_match() detects a recursion loop within the pattern. Specifically, it means that either the whole pat- - tern or a capture group has been called recursively for the second time - at the same position in the subject string. Some simple patterns that + tern or a subpattern has been called recursively for the second time at + the same position in the subject string. Some simple patterns that might do this are detected and faulted at compile time, but more com- plicated cases, in particular mutual recursions between two different - groups, cannot be detected until matching is attempted. + subpatterns, cannot be detected until matching is attempted. OBTAINING A TEXTUAL ERROR MESSAGE @@ -3015,7 +2947,7 @@ EXTRACTING CAPTURED SUBSTRINGS BY NUMBER copies it into new memory, obtained using the same memory allocation function that was used for the match data block. The first two argu- ments of these functions are a pointer to the match data block and a - capture group number. + capturing group number. The final arguments of pcre2_substring_copy_bynumber() are a pointer to the buffer and a pointer to a variable that contains its length in code @@ -3085,11 +3017,12 @@ EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS should be freed by calling pcre2_substring_list_free(). If this function encounters a substring that is unset, which can happen - when capture group number n+1 matches some part of the subject, but - group n has not been used at all, it returns an empty string. This can - be distinguished from a genuine zero-length substring by inspecting the - appropriate offset in the ovector, which contain PCRE2_UNSET for unset - substrings, or by calling pcre2_substring_length_bynumber(). + when capturing subpattern number n+1 matches some part of the subject, + but subpattern n has not been used at all, it returns an empty string. + This can be distinguished from a genuine zero-length substring by + inspecting the appropriate offset in the ovector, which contain + PCRE2_UNSET for unset substrings, or by calling pcre2_sub- + string_length_bynumber(). EXTRACTING CAPTURED SUBSTRINGS BY NAME @@ -3108,27 +3041,26 @@ EXTRACTING CAPTURED SUBSTRINGS BY NAME void pcre2_substring_free(PCRE2_UCHAR *buffer); - To extract a substring by name, you first have to find associated num- + To extract a substring by name, you first have to find associated num- ber. For example, for this pattern: (a+)b(?<xxx>\d+)... - the number of the capture group called "xxx" is 2. If the name is known - to be unique (PCRE2_DUPNAMES was not set), you can find the number from + the number of the subpattern called "xxx" is 2. If the name is known to + be unique (PCRE2_DUPNAMES was not set), you can find the number from the name by calling pcre2_substring_number_from_name(). The first argu- - ment is the compiled pattern, and the second is the name. The yield of - the function is the group number, PCRE2_ERROR_NOSUBSTRING if there is - no group with that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if there is - more than one group with that name. Given the number, you can extract - the substring directly from the ovector, or use one of the "bynumber" - functions described above. - - For convenience, there are also "byname" functions that correspond to - the "bynumber" functions, the only difference being that the second - argument is a name instead of a number. If PCRE2_DUPNAMES is set and + ment is the compiled pattern, and the second is the name. The yield of + the function is the subpattern number, PCRE2_ERROR_NOSUBSTRING if there + is no subpattern of that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if + there is more than one subpattern of that name. Given the number, you + can extract the substring directly from the ovector, or use one of the + "bynumber" functions described above. + + For convenience, there are also "byname" functions that correspond to + the "bynumber" functions, the only difference being that the second + argument is a name instead of a number. If PCRE2_DUPNAMES is set and there are duplicate names, these functions scan all the groups with the - given name, and return the captured substring from the first named - group that is set. + given name, and return the first named string that is set. If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is returned. If all groups with the name have numbers that are greater @@ -3136,12 +3068,12 @@ EXTRACTING CAPTURED SUBSTRINGS BY NAME returned. If there is at least one group with a slot in the ovector, but no group is found to be set, PCRE2_ERROR_UNSET is returned. - Warning: If the pattern uses the (?| feature to set up multiple capture - groups with the same number, as described in the section on duplicate - group numbers in the pcre2pattern page, you cannot use names to distin- - guish the different capture groups, because names are not included in - the compiled code. The matching process uses only numbers. For this - reason, the use of different names for groups with the same number + Warning: If the pattern uses the (?| feature to set up multiple subpat- + terns with the same number, as described in the section on duplicate + subpattern numbers in the pcre2pattern page, you cannot use names to + distinguish the different subpatterns, because names are not included + in the compiled code. The matching process uses only numbers. For this + reason, the use of different names for subpatterns of the same number causes an error at compile time. @@ -3151,22 +3083,18 @@ CREATING A NEW STRING WITH SUBSTITUTIONS PCRE2_SIZE length, PCRE2_SIZE startoffset, uint32_t options, pcre2_match_data *match_data, pcre2_match_context *mcontext, PCRE2_SPTR replacement, - PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer, + PCRE2_SIZE rlength, PCRE2_UCHAR *outputbufferP, PCRE2_SIZE *outlengthptr); This function calls pcre2_match() and then makes a copy of the subject - string in outputbuffer, replacing one or more parts that were matched - with the replacement string, whose length is supplied in rlength. This - can be given as PCRE2_ZERO_TERMINATED for a zero-terminated string. - The default is to perform just one replacement, but there is an option - that requests multiple replacements (see PCRE2_SUBSTITUTE_GLOBAL below - for details). - - Matches in which a \K item in a lookahead in the pattern causes the - match to end before it starts are not supported, and give rise to an - error return. For global replacements, matches in which \K in a lookbe- - hind causes the match to start earlier than the point that was reached - in the previous iteration are also not supported. + string in outputbuffer, replacing the part that was matched with the + replacement string, whose length is supplied in rlength. This can be + given as PCRE2_ZERO_TERMINATED for a zero-terminated string. Matches in + which a \K item in a lookahead in the pattern causes the match to end + before it starts are not supported, and give rise to an error return. + For global replacements, matches in which \K in a lookbehind causes the + match to start earlier than the point that was reached in the previous + iteration are also not supported. The first seven arguments of pcre2_substitute() are the same as for pcre2_match(), except that the partial matching options are not permit- @@ -3176,9 +3104,9 @@ CREATING A NEW STRING WITH SUBSTITUTIONS were used to allocate memory for the compiled code. If an external match_data block is provided, its contents afterwards - are those set by the final call to pcre2_match(). For global changes, - this will have ended in a matching error. The contents of the ovector - within the match data block may or may not have been changed. + are those set by the final call to pcre2_match(), which will have ended + in a matching error. The contents of the ovector within the match data + block may or may not have been changed. The outlengthptr argument must point to a variable that contains the length, in code units, of the output buffer. If the function is suc- @@ -3200,13 +3128,13 @@ CREATING A NEW STRING WITH SUBSTITUTIONS In the replacement string, which is interpreted as a UTF string in UTF mode, and is checked for UTF validity unless the PCRE2_NO_UTF_CHECK option is set, a dollar character is an escape character that can spec- - ify the insertion of characters from capture groups or names from - (*MARK) or other control verbs in the pattern. The following forms are + ify the insertion of characters from capturing groups or (*MARK), + (*PRUNE), or (*THEN) items in the pattern. The following forms are always recognized: $$ insert a dollar character $<n> or ${<n>} insert the contents of group <n> - $*MARK or ${*MARK} insert a control verb name + $*MARK or ${*MARK} insert a (*MARK), (*PRUNE), or (*THEN) name Either a group number or a group name can be given for <n>. Curly brackets are required only if the following character would be inter- @@ -3215,30 +3143,31 @@ CREATING A NEW STRING WITH SUBSTITUTIONS matched with "=abc=" and the replacement string "+$1$0$1+", the result is "=+babcb+=". - $*MARK inserts the name from the last encountered backtracking control - verb on the matching path that has a name. (*MARK) must always include - a name, but the other verbs need not. For example, in the case of - (*MARK:A)(*PRUNE) the name inserted is "A", but for (*MARK:A)(*PRUNE:B) - the relevant name is "B". This facility can be used to perform simple - simultaneous substitutions, as this pcre2test example shows: + $*MARK inserts the name from the last encountered (*MARK), (*PRUNE), or + (*THEN) on the matching path that has a name. (*MARK) must always + include a name, but (*PRUNE) and (*THEN) need not. For example, in the + case of (*MARK:A)(*PRUNE) the name inserted is "A", but for + (*MARK:A)(*PRUNE:B) the relevant name is "B". This facility can be + used to perform simple simultaneous substitutions, as this pcre2test + example shows: /(*MARK:pear)apple|(*MARK:orange)lemon/g,replace=${*MARK} apple lemon 2: pear orange - As well as the usual options for pcre2_match(), a number of additional + As well as the usual options for pcre2_match(), a number of additional options can be set in the options argument of pcre2_substitute(). PCRE2_SUBSTITUTE_GLOBAL causes the function to iterate over the subject - string, replacing every matching substring. If this option is not set, - only the first matching substring is replaced. The search for matches - takes place in the original subject string (that is, previous replace- - ments do not affect it). Iteration is implemented by advancing the - startoffset value for each search, which is always passed the entire + string, replacing every matching substring. If this option is not set, + only the first matching substring is replaced. The search for matches + takes place in the original subject string (that is, previous replace- + ments do not affect it). Iteration is implemented by advancing the + startoffset value for each search, which is always passed the entire subject string. If an offset limit is set in the match context, search- ing stops when that limit is reached. - You can restrict the effect of a global substitution to a portion of + You can restrict the effect of a global substitution to a portion of the subject string by setting either or both of startoffset and an off- set limit. Here is a pcre2test example: @@ -3246,35 +3175,36 @@ CREATING A NEW STRING WITH SUBSTITUTIONS ABC ABC ABC ABC\=offset=3,offset_limit=12 2: ABC A!C A!C ABC - When continuing with global substitutions after matching a substring + When continuing with global substitutions after matching a substring with zero length, an attempt to find a non-empty match at the same off- set is performed. If this is not successful, the offset is advanced by one character except when CRLF is a valid newline sequence and the next - two characters are CR, LF. In this case, the offset is advanced by two + two characters are CR, LF. In this case, the offset is advanced by two characters. - PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output + PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output buffer is too small. The default action is to return PCRE2_ERROR_NOMEM- - ORY immediately. If this option is set, however, pcre2_substitute() + ORY immediately. If this option is set, however, pcre2_substitute() continues to go through the motions of matching and substituting (with- - out, of course, writing anything) in order to compute the size of buf- - fer that is needed. This value is passed back via the outlengthptr - variable, with the result of the function still being + out, of course, writing anything) in order to compute the size of buf- + fer that is needed. This value is passed back via the outlengthptr + variable, with the result of the function still being PCRE2_ERROR_NOMEMORY. - Passing a buffer size of zero is a permitted way of finding out how - much memory is needed for given substitution. However, this does mean + Passing a buffer size of zero is a permitted way of finding out how + much memory is needed for given substitution. However, this does mean that the entire operation is carried out twice. Depending on the appli- - cation, it may be more efficient to allocate a large buffer and free - the excess afterwards, instead of using PCRE2_SUBSTITUTE_OVER- + cation, it may be more efficient to allocate a large buffer and free + the excess afterwards, instead of using PCRE2_SUBSTITUTE_OVER- FLOW_LENGTH. - PCRE2_SUBSTITUTE_UNKNOWN_UNSET causes references to capture groups that - do not appear in the pattern to be treated as unset groups. This option - should be used with care, because it means that a typo in a group name - or number no longer causes the PCRE2_ERROR_NOSUBSTRING error. + PCRE2_SUBSTITUTE_UNKNOWN_UNSET causes references to capturing groups + that do not appear in the pattern to be treated as unset groups. This + option should be used with care, because it means that a typo in a + group name or number no longer causes the PCRE2_ERROR_NOSUBSTRING + error. - PCRE2_SUBSTITUTE_UNSET_EMPTY causes unset capture groups (including + PCRE2_SUBSTITUTE_UNSET_EMPTY causes unset capturing groups (including unknown groups when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) to be treated as empty strings when inserted as described above. If this option is not set, an attempt to insert an unset group causes the @@ -3300,18 +3230,16 @@ CREATING A NEW STRING WITH SUBSTITUTIONS no case forcing. The sequences \u and \l force the next character (if it is a letter) to upper or lower case, respectively, and then the state automatically reverts to no case forcing. Case forcing applies to - all inserted characters, including those from capture groups and let- + all inserted characters, including those from captured groups and let- ters within \Q...\E quoted sequences. Note that case forcing sequences such as \U...\E do not nest. For exam- ple, the result of processing "\Uaa\LBB\Ecc\E" is "AAbbcc"; the final - \E has no effect. Note also that the PCRE2_ALT_BSUX and - PCRE2_EXTRA_ALT_BSUX options do not apply to not apply to replacement - strings. + \E has no effect. The second effect of setting PCRE2_SUBSTITUTE_EXTENDED is to add more - flexibility to capture group substitution. The syntax is similar to - that used by Bash: + flexibility to group substitution. The syntax is similar to that used + by Bash: ${<n>:-<string>} ${<n>:+<string1>:<string2>} @@ -3340,8 +3268,8 @@ CREATING A NEW STRING WITH SUBSTITUTIONS substitutions. However, PCRE2_SUBSTITUTE_UNKNOWN_UNSET does cause unknown groups in the extended syntax forms to be treated as unset. - If successful, pcre2_substitute() returns the number of successful - matches. This may be zero if no matches were found, and is never + If successful, pcre2_substitute() returns the number of replacements + that were made. This may be zero if no matches were found, and is never greater than 1 unless PCRE2_SUBSTITUTE_GLOBAL is set. In the event of an error, a negative error code is returned. Except for @@ -3374,117 +3302,62 @@ CREATING A NEW STRING WITH SUBSTITUTIONS obtained by calling the pcre2_get_error_message() function (see "Obtaining a textual error message" above). - Substitution callouts - int pcre2_set_substitute_callout(pcre2_match_context *mcontext, - int (*callout_function)(pcre2_substitute_callout_block *, void *), - void *callout_data); - - The pcre2_set_substitution_callout() function can be used to specify a - callout function for pcre2_substitute(). This information is passed in - a match context. The callout function is called after each substitution - has been processed, but it can cause the replacement not to happen. The - callout function is not called for simulated substitutions that happen - as a result of the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option. - - The first argument of the callout function is a pointer to a substitute - callout block structure, which contains the following fields, not nec- - essarily in this order: - - uint32_t version; - uint32_t subscount; - PCRE2_SPTR input; - PCRE2_SPTR output; - PCRE2_SIZE *ovector; - uint32_t oveccount; - PCRE2_SIZE output_offsets[2]; - - The version field contains the version number of the block format. The - current version is 0. The version number will increase in future if - more fields are added, but the intention is never to remove any of the - existing fields. - - The subscount field is the number of the current match. It is 1 for the - first callout, 2 for the second, and so on. The input and output point- - ers are copies of the values passed to pcre2_substitute(). - - The ovector field points to the ovector, which contains the result of - the most recent match. The oveccount field contains the number of pairs - that are set in the ovector, and is always greater than zero. - - The output_offsets vector contains the offsets of the replacement in - the output string. This has already been processed for dollar and (if - requested) backslash substitutions as described above. - - The second argument of the callout function is the value passed as - callout_data when the function was registered. The value returned by - the callout function is interpreted as follows: - - If the value is zero, the replacement is accepted, and, if PCRE2_SUB- - STITUTE_GLOBAL is set, processing continues with a search for the next - match. If the value is not zero, the current replacement is not - accepted. If the value is greater than zero, processing continues when - PCRE2_SUBSTITUTE_GLOBAL is set. Otherwise (the value is less than zero - or PCRE2_SUBSTITUTE_GLOBAL is not set), the the rest of the input is - copied to the output and the call to pcre2_substitute() exits, return- - ing the number of matches so far. - - -DUPLICATE CAPTURE GROUP NAMES +DUPLICATE SUBPATTERN NAMES int pcre2_substring_nametable_scan(const pcre2_code *code, PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last); - When a pattern is compiled with the PCRE2_DUPNAMES option, names for - capture groups are not required to be unique. Duplicate names are - always allowed for groups with the same number, created by using the - (?| feature. Indeed, if such groups are named, they are required to use - the same names. + When a pattern is compiled with the PCRE2_DUPNAMES option, names for + subpatterns are not required to be unique. Duplicate names are always + allowed for subpatterns with the same number, created by using the (?| + feature. Indeed, if such subpatterns are named, they are required to + use the same names. - Normally, patterns that use duplicate names are such that in any one - match, only one of each set of identically-named groups participates. - An example is shown in the pcre2pattern documentation. + Normally, patterns with duplicate names are such that in any one match, + only one of the named subpatterns participates. An example is shown in + the pcre2pattern documentation. - When duplicates are present, pcre2_substring_copy_byname() and - pcre2_substring_get_byname() return the first substring corresponding - to the given name that is set. Only if none are set is - PCRE2_ERROR_UNSET is returned. The pcre2_substring_number_from_name() + When duplicates are present, pcre2_substring_copy_byname() and + pcre2_substring_get_byname() return the first substring corresponding + to the given name that is set. Only if none are set is + PCRE2_ERROR_UNSET is returned. The pcre2_substring_number_from_name() function returns the error PCRE2_ERROR_NOUNIQUESUBSTRING when there are duplicate names. - If you want to get full details of all captured substrings for a given - name, you must use the pcre2_substring_nametable_scan() function. The - first argument is the compiled pattern, and the second is the name. If - the third and fourth arguments are NULL, the function returns a group + If you want to get full details of all captured substrings for a given + name, you must use the pcre2_substring_nametable_scan() function. The + first argument is the compiled pattern, and the second is the name. If + the third and fourth arguments are NULL, the function returns a group number for a unique name, or PCRE2_ERROR_NOUNIQUESUBSTRING otherwise. When the third and fourth arguments are not NULL, they must be pointers - to variables that are updated by the function. After it has run, they + to variables that are updated by the function. After it has run, they point to the first and last entries in the name-to-number table for the - given name, and the function returns the length of each entry in code - units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are + given name, and the function returns the length of each entry in code + units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are no entries for the given name. The format of the name table is described above in the section entitled - Information about a pattern. Given all the relevant entries for the - name, you can extract each of their numbers, and hence the captured + Information about a pattern. Given all the relevant entries for the + name, you can extract each of their numbers, and hence the captured data. FINDING ALL POSSIBLE MATCHES AT ONE POSITION - The traditional matching function uses a similar algorithm to Perl, - which stops when it finds the first match at a given point in the sub- + The traditional matching function uses a similar algorithm to Perl, + which stops when it finds the first match at a given point in the sub- ject. If you want to find all possible matches, or the longest possible - match at a given position, consider using the alternative matching - function (see below) instead. If you cannot use the alternative func- + match at a given position, consider using the alternative matching + function (see below) instead. If you cannot use the alternative func- tion, you can kludge it up by making use of the callout facility, which is described in the pcre2callout documentation. What you have to do is to insert a callout right at the end of the pat- - tern. When your callout function is called, extract and save the cur- - rent matched substring. Then return 1, which forces pcre2_match() to - backtrack and try other alternatives. Ultimately, when it runs out of + tern. When your callout function is called, extract and save the cur- + rent matched substring. Then return 1, which forces pcre2_match() to + backtrack and try other alternatives. Ultimately, when it runs out of matches, pcre2_match() will yield PCRE2_ERROR_NOMATCH. @@ -3496,26 +3369,26 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION pcre2_match_context *mcontext, int *workspace, PCRE2_SIZE wscount); - The function pcre2_dfa_match() is called to match a subject string - against a compiled pattern, using a matching algorithm that scans the + The function pcre2_dfa_match() is called to match a subject string + against a compiled pattern, using a matching algorithm that scans the subject string just once (not counting lookaround assertions), and does - not backtrack. This has different characteristics to the normal algo- - rithm, and is not compatible with Perl. Some of the features of PCRE2 - patterns are not supported. Nevertheless, there are times when this - kind of matching can be useful. For a discussion of the two matching + not backtrack. This has different characteristics to the normal algo- + rithm, and is not compatible with Perl. Some of the features of PCRE2 + patterns are not supported. Nevertheless, there are times when this + kind of matching can be useful. For a discussion of the two matching algorithms, and a list of features that pcre2_dfa_match() does not sup- port, see the pcre2matching documentation. - The arguments for the pcre2_dfa_match() function are the same as for + The arguments for the pcre2_dfa_match() function are the same as for pcre2_match(), plus two extras. The ovector within the match data block is used in a different way, and this is described below. The other com- - mon arguments are used in the same way as for pcre2_match(), so their + mon arguments are used in the same way as for pcre2_match(), so their description is not repeated here. - The two additional arguments provide workspace for the function. The - workspace vector should contain at least 20 elements. It is used for + The two additional arguments provide workspace for the function. The + workspace vector should contain at least 20 elements. It is used for keeping track of multiple paths through the pattern tree. More - workspace is needed for patterns and subjects where there are a lot of + workspace is needed for patterns and subjects where there are a lot of potential matches. Here is an example of a simple call to pcre2_dfa_match(): @@ -3535,14 +3408,13 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION Option bits for pcre_dfa_match() - The unused bits of the options argument for pcre2_dfa_match() must be - zero. The only bits that may be set are PCRE2_ANCHORED, - PCRE2_COPY_MATCHED_SUBJECT, PCRE2_ENDANCHORED, PCRE2_NOTBOL, - PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, - PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, PCRE2_PARTIAL_SOFT, - PCRE2_DFA_SHORTEST, and PCRE2_DFA_RESTART. All but the last four of - these are exactly the same as for pcre2_match(), so their description - is not repeated here. + The unused bits of the options argument for pcre2_dfa_match() must be + zero. The only bits that may be set are PCRE2_ANCHORED, PCRE2_ENDAN- + CHORED, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, + PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, + PCRE2_PARTIAL_SOFT, PCRE2_DFA_SHORTEST, and PCRE2_DFA_RESTART. All but + the last four of these are exactly the same as for pcre2_match(), so + their description is not repeated here. PCRE2_PARTIAL_HARD PCRE2_PARTIAL_SOFT @@ -3602,8 +3474,8 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION which is the number of matched substrings. The offsets of the sub- strings are returned in the ovector, and can be extracted by number in the same way as for pcre2_match(), but the numbers bear no relation to - any capture groups that may exist in the pattern, because DFA matching - does not support capturing. + any capturing groups that may exist in the pattern, because DFA match- + ing does not support group capture. Calls to the convenience functions that extract substrings by name return the error PCRE2_ERROR_DFA_UFUNC (unsupported function) if used @@ -3640,7 +3512,7 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION This return is given if pcre2_dfa_match() encounters a condition item that uses a backreference for the condition, or a test for recursion in - a specific capture group. These are not supported. + a specific group. These are not supported. PCRE2_ERROR_DFA_WSSIZE @@ -3649,23 +3521,22 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION PCRE2_ERROR_DFA_RECURSE - When a recursion or subroutine call is processed, the matching function - calls itself recursively, using private memory for the ovector and - workspace. This error is given if the internal ovector is not large - enough. This should be extremely rare, as a vector of size 1000 is - used. + When a recursive subpattern is processed, the matching function calls + itself recursively, using private memory for the ovector and workspace. + This error is given if the internal ovector is not large enough. This + should be extremely rare, as a vector of size 1000 is used. PCRE2_ERROR_DFA_BADRESTART - When pcre2_dfa_match() is called with the PCRE2_DFA_RESTART option, - some plausibility checks are made on the contents of the workspace, - which should contain data about the previous partial match. If any of + When pcre2_dfa_match() is called with the PCRE2_DFA_RESTART option, + some plausibility checks are made on the contents of the workspace, + which should contain data about the previous partial match. If any of these checks fail, this error is given. SEE ALSO - pcre2build(3), pcre2callout(3), pcre2demo(3), pcre2matching(3), + pcre2build(3), pcre2callout(3), pcre2demo(3), pcre2matching(3), pcre2partial(3), pcre2posix(3), pcre2sample(3), pcre2unicode(3). @@ -3678,8 +3549,8 @@ AUTHOR REVISION - Last updated: 14 February 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 07 September 2018 + Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ @@ -4027,48 +3898,45 @@ USING EBCDIC CODE PCRE2GREP SUPPORT FOR EXTERNAL SCRIPTS - By default pcre2grep supports the use of callouts with string arguments - within the patterns it is matching. There are two kinds: one that gen- - erates output using local code, and another that calls an external pro- - gram or script. If --disable-pcre2grep-callout-fork is added to the - configure command, only the first kind of callout is supported; if - --disable-pcre2grep-callout is used, all callouts are completely - ignored. For more details of pcre2grep callouts, see the pcre2grep doc- - umentation. + By default, on non-Windows systems, pcre2grep supports the use of call- + outs with string arguments within the patterns it is matching, in order + to run external scripts. For details, see the pcre2grep documentation. + This support can be disabled by adding --disable-pcre2grep-callout to + the configure command. PCRE2GREP OPTIONS FOR COMPRESSED FILE SUPPORT - By default, pcre2grep reads all files as plain text. You can build it - so that it recognizes files whose names end in .gz or .bz2, and reads + By default, pcre2grep reads all files as plain text. You can build it + so that it recognizes files whose names end in .gz or .bz2, and reads them with libz or libbz2, respectively, by adding one or both of --enable-pcre2grep-libz --enable-pcre2grep-libbz2 to the configure command. These options naturally require that the rel- - evant libraries are installed on your system. Configuration will fail + evant libraries are installed on your system. Configuration will fail if they are not. PCRE2GREP BUFFER SIZE - pcre2grep uses an internal buffer to hold a "window" on the file it is + pcre2grep uses an internal buffer to hold a "window" on the file it is scanning, in order to be able to output "before" and "after" lines when it finds a match. The default starting size of the buffer is 20KiB. The - buffer itself is three times this size, but because of the way it is + buffer itself is three times this size, but because of the way it is used for holding "before" lines, the longest line that is guaranteed to be processable is the notional buffer size. If a longer line is encoun- - tered, pcre2grep automatically expands the buffer, up to a specified - maximum size, whose default is 1MiB or the starting size, whichever is - the larger. You can change the default parameter values by adding, for + tered, pcre2grep automatically expands the buffer, up to a specified + maximum size, whose default is 1MiB or the starting size, whichever is + the larger. You can change the default parameter values by adding, for example, --with-pcre2grep-bufsize=51200 --with-pcre2grep-max-bufsize=2097152 - to the configure command. The caller of pcre2grep can override these - values by using --buffer-size and --max-buffer-size on the command + to the configure command. The caller of pcre2grep can override these + values by using --buffer-size and --max-buffer-size on the command line. @@ -4079,26 +3947,26 @@ PCRE2TEST OPTION FOR LIBREADLINE SUPPORT --enable-pcre2test-libreadline --enable-pcre2test-libedit - to the configure command, pcre2test is linked with the libreadline + to the configure command, pcre2test is linked with the libreadline orlibedit library, respectively, and when its input is from a terminal, - it reads it using the readline() function. This provides line-editing - and history facilities. Note that libreadline is GPL-licensed, so if - you distribute a binary of pcre2test linked in this way, there may be + it reads it using the readline() function. This provides line-editing + and history facilities. Note that libreadline is GPL-licensed, so if + you distribute a binary of pcre2test linked in this way, there may be licensing issues. These can be avoided by linking instead with libedit, which has a BSD licence. - Setting --enable-pcre2test-libreadline causes the -lreadline option to - be added to the pcre2test build. In many operating environments with a - sytem-installed readline library this is sufficient. However, in some + Setting --enable-pcre2test-libreadline causes the -lreadline option to + be added to the pcre2test build. In many operating environments with a + sytem-installed readline library this is sufficient. However, in some environments (e.g. if an unmodified distribution version of readline is - in use), some extra configuration may be necessary. The INSTALL file + in use), some extra configuration may be necessary. The INSTALL file for libreadline says this: "Readline uses the termcap functions, but does not link with the termcap or curses library itself, allowing applications which link with readline the to choose an appropriate library." - If your environment has not been set up so that an appropriate library + If your environment has not been set up so that an appropriate library is automatically included, you may need to add something like LIBS="-ncurses" @@ -4112,7 +3980,7 @@ INCLUDING DEBUGGING CODE --enable-debug - to the configure command, additional debugging code is included in the + to the configure command, additional debugging code is included in the build. This feature is intended for use by the PCRE2 maintainers. @@ -4122,15 +3990,15 @@ DEBUGGING WITH VALGRIND SUPPORT --enable-valgrind - to the configure command, PCRE2 will use valgrind annotations to mark - certain memory regions as unaddressable. This allows it to detect - invalid memory accesses, and is mostly useful for debugging PCRE2 + to the configure command, PCRE2 will use valgrind annotations to mark + certain memory regions as unaddressable. This allows it to detect + invalid memory accesses, and is mostly useful for debugging PCRE2 itself. CODE COVERAGE REPORTING - If your C compiler is gcc, you can build a version of PCRE2 that can + If your C compiler is gcc, you can build a version of PCRE2 that can generate a code coverage report for its test suite. To enable this, you must install lcov version 1.6 or above. Then specify @@ -4139,20 +4007,20 @@ CODE COVERAGE REPORTING to the configure command and build PCRE2 in the usual way. Note that using ccache (a caching C compiler) is incompatible with code - coverage reporting. If you have configured ccache to run automatically + coverage reporting. If you have configured ccache to run automatically on your system, you must set the environment variable CCACHE_DISABLE=1 before running make to build PCRE2, so that ccache is not used. - When --enable-coverage is used, the following addition targets are + When --enable-coverage is used, the following addition targets are added to the Makefile: make coverage - This creates a fresh coverage report for the PCRE2 test suite. It is - equivalent to running "make coverage-reset", "make coverage-baseline", + This creates a fresh coverage report for the PCRE2 test suite. It is + equivalent to running "make coverage-reset", "make coverage-baseline", "make check", and then "make coverage-report". make coverage-reset @@ -4169,71 +4037,56 @@ CODE COVERAGE REPORTING make coverage-clean-report - This removes the generated coverage report without cleaning the cover- + This removes the generated coverage report without cleaning the cover- age data itself. make coverage-clean-data - This removes the captured coverage data without removing the coverage + This removes the captured coverage data without removing the coverage files created at compile time (*.gcno). make coverage-clean - This cleans all coverage data including the generated coverage report. - For more information about code coverage, see the gcov and lcov docu- + This cleans all coverage data including the generated coverage report. + For more information about code coverage, see the gcov and lcov docu- mentation. -DISABLING THE Z AND T FORMATTING MODIFIERS - - The C99 standard defines formatting modifiers z and t for size_t and - ptrdiff_t values, respectively. By default, PCRE2 uses these modifiers - in environments other than Microsoft Visual Studio when __STDC_VER- - SION__ is defined and has a value greater than or equal to 199901L - (indicating C99). However, there is at least one environment that - claims to be C99 but does not support these modifiers. If - - --disable-percent-zt - - is specified, no use is made of the z or t modifiers. Instead or %td or - %zu, %lu is used, with a cast for size_t values. - - SUPPORT FOR FUZZERS - There is a special option for use by people who want to run fuzzing + There is a special option for use by people who want to run fuzzing tests on PCRE2: --enable-fuzz-support At present this applies only to the 8-bit library. If set, it causes an - extra library called libpcre2-fuzzsupport.a to be built, but not - installed. This contains a single function called LLVMFuzzerTestOneIn- - put() whose arguments are a pointer to a string and the length of the - string. When called, this function tries to compile the string as a - pattern, and if that succeeds, to match it. This is done both with no - options and with some random options bits that are generated from the + extra library called libpcre2-fuzzsupport.a to be built, but not + installed. This contains a single function called LLVMFuzzerTestOneIn- + put() whose arguments are a pointer to a string and the length of the + string. When called, this function tries to compile the string as a + pattern, and if that succeeds, to match it. This is done both with no + options and with some random options bits that are generated from the string. - Setting --enable-fuzz-support also causes a binary called pcre2fuz- - zcheck to be created. This is normally run under valgrind or used when + Setting --enable-fuzz-support also causes a binary called pcre2fuz- + zcheck to be created. This is normally run under valgrind or used when PCRE2 is compiled with address sanitizing enabled. It calls the fuzzing - function and outputs information about what it is doing. The input - strings are specified by arguments: if an argument starts with "=" the - rest of it is a literal input string. Otherwise, it is assumed to be a + function and outputs information about what it is doing. The input + strings are specified by arguments: if an argument starts with "=" the + rest of it is a literal input string. Otherwise, it is assumed to be a file name, and the contents of the file are the test string. OBSOLETE OPTION - In versions of PCRE2 prior to 10.30, there were two ways of handling - backtracking in the pcre2_match() function. The default was to use the + In versions of PCRE2 prior to 10.30, there were two ways of handling + backtracking in the pcre2_match() function. The default was to use the system stack, but if --disable-stack-for-recursion - was set, memory on the heap was used. From release 10.30 onwards this - has changed (the stack is no longer used) and this option now does + was set, memory on the heap was used. From release 10.30 onwards this + has changed (the stack is no longer used) and this option now does nothing except give a warning. @@ -4251,8 +4104,8 @@ AUTHOR REVISION - Last updated: 03 March 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 26 April 2018 + Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ @@ -4282,26 +4135,21 @@ DESCRIPTION its entry point in a match context (see pcre2_set_callout() in the pcre2api documentation). - When using the pcre2_substitute() function, an additional callout fea- - ture is available. This does a callout after each change to the subject - string and is described in the pcre2api documentation; the rest of this - document is concerned with callouts during pattern matching. - - Within a regular expression, (?C<arg>) indicates a point at which the - external function is to be called. Different callout points can be - identified by putting a number less than 256 after the letter C. The - default value is zero. Alternatively, the argument may be a delimited - string. The starting delimiter must be one of ` ' " ^ % # $ { and the + Within a regular expression, (?C<arg>) indicates a point at which the + external function is to be called. Different callout points can be + identified by putting a number less than 256 after the letter C. The + default value is zero. Alternatively, the argument may be a delimited + string. The starting delimiter must be one of ` ' " ^ % # $ { and the ending delimiter is the same as the start, except for {, where the end- - ing delimiter is }. If the ending delimiter is needed within the - string, it must be doubled. For example, this pattern has two callout + ing delimiter is }. If the ending delimiter is needed within the + string, it must be doubled. For example, this pattern has two callout points: (?C1)abc(?C"some ""arbitrary"" text")def If the PCRE2_AUTO_CALLOUT option bit is set when a pattern is compiled, - PCRE2 automatically inserts callouts, all with number 255, before each - item in the pattern except for immediately before or after an explicit + PCRE2 automatically inserts callouts, all with number 255, before each + item in the pattern except for immediately before or after an explicit callout. For example, if PCRE2_AUTO_CALLOUT is used with the pattern A(?C3)B @@ -4318,36 +4166,36 @@ DESCRIPTION (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255) - Notice that there is a callout before and after each parenthesis and + Notice that there is a callout before and after each parenthesis and alternation bar. If the pattern contains a conditional group whose con- - dition is an assertion, an automatic callout is inserted immediately - before the condition. Such a callout may also be inserted explicitly, + dition is an assertion, an automatic callout is inserted immediately + before the condition. Such a callout may also be inserted explicitly, for example: (?(?C9)(?=a)ab|de) (?(?C%text%)(?!=d)ab|de) - This applies only to assertion conditions (because they are themselves + This applies only to assertion conditions (because they are themselves independent groups). - Callouts can be useful for tracking the progress of pattern matching. + Callouts can be useful for tracking the progress of pattern matching. The pcre2test program has a pattern qualifier (/auto_callout) that sets - automatic callouts. When any callouts are present, the output from - pcre2test indicates how the pattern is being matched. This is useful - information when you are trying to optimize the performance of a par- + automatic callouts. When any callouts are present, the output from + pcre2test indicates how the pattern is being matched. This is useful + information when you are trying to optimize the performance of a par- ticular pattern. MISSING CALLOUTS - You should be aware that, because of optimizations in the way PCRE2 + You should be aware that, because of optimizations in the way PCRE2 compiles and matches patterns, callouts sometimes do not happen exactly as you might expect. Auto-possessification At compile time, PCRE2 "auto-possessifies" repeated items when it knows - that what follows cannot be part of the repeat. For example, a+[bc] is - compiled as if it were a++[bc]. The pcre2test output when this pattern + that what follows cannot be part of the repeat. For example, a+[bc] is + compiled as if it were a++[bc]. The pcre2test output when this pattern is compiled with PCRE2_ANCHORED and PCRE2_AUTO_CALLOUT and then applied to the string "aaaa" is: @@ -4356,11 +4204,11 @@ MISSING CALLOUTS +2 ^ ^ [bc] No match - This indicates that when matching [bc] fails, there is no backtracking + This indicates that when matching [bc] fails, there is no backtracking into a+ (because it is being treated as a++) and therefore the callouts - that would be taken for the backtracks do not occur. You can disable - the auto-possessify feature by passing PCRE2_NO_AUTO_POSSESS to - pcre2_compile(), or starting the pattern with (*NO_AUTO_POSSESS). In + that would be taken for the backtracks do not occur. You can disable + the auto-possessify feature by passing PCRE2_NO_AUTO_POSSESS to + pcre2_compile(), or starting the pattern with (*NO_AUTO_POSSESS). In this case, the output changes to this: --->aaaa @@ -4377,19 +4225,19 @@ MISSING CALLOUTS Automatic .* anchoring By default, an optimization is applied when .* is the first significant - item in a pattern. If PCRE2_DOTALL is set, so that the dot can match - any character, the pattern is automatically anchored. If PCRE2_DOTALL - is not set, a match can start only after an internal newline or at the + item in a pattern. If PCRE2_DOTALL is set, so that the dot can match + any character, the pattern is automatically anchored. If PCRE2_DOTALL + is not set, a match can start only after an internal newline or at the beginning of the subject, and pcre2_compile() remembers this. If a pat- - tern has more than one top-level branch, automatic anchoring occurs if + tern has more than one top-level branch, automatic anchoring occurs if all branches are anchorable. - This optimization is disabled, however, if .* is in an atomic group or - if there is a backreference to the capture group in which it appears. - It is also disabled if the pattern contains (*PRUNE) or (*SKIP). How- + This optimization is disabled, however, if .* is in an atomic group or + if there is a backreference to the capturing group in which it appears. + It is also disabled if the pattern contains (*PRUNE) or (*SKIP). How- ever, the presence of callouts does not affect it. - For example, if the pattern .*\d is compiled with PCRE2_AUTO_CALLOUT + For example, if the pattern .*\d is compiled with PCRE2_AUTO_CALLOUT and applied to the string "aa", the pcre2test output is: --->aa @@ -4399,10 +4247,10 @@ MISSING CALLOUTS +2 ^ \d No match - This shows that all match attempts start at the beginning of the sub- - ject. In other words, the pattern is anchored. You can disable this - optimization by passing PCRE2_NO_DOTSTAR_ANCHOR to pcre2_compile(), or - starting the pattern with (*NO_DOTSTAR_ANCHOR). In this case, the out- + This shows that all match attempts start at the beginning of the sub- + ject. In other words, the pattern is anchored. You can disable this + optimization by passing PCRE2_NO_DOTSTAR_ANCHOR to pcre2_compile(), or + starting the pattern with (*NO_DOTSTAR_ANCHOR). In this case, the out- put changes to: --->aa @@ -4415,42 +4263,42 @@ MISSING CALLOUTS +2 ^ \d No match - This shows more match attempts, starting at the second subject charac- - ter. Another optimization, described in the next section, means that + This shows more match attempts, starting at the second subject charac- + ter. Another optimization, described in the next section, means that there is no subsequent attempt to match with an empty subject. Other optimizations - Other optimizations that provide fast "no match" results also affect + Other optimizations that provide fast "no match" results also affect callouts. For example, if the pattern is ab(?C4)cd - PCRE2 knows that any matching string must contain the letter "d". If - the subject string is "abyz", the lack of "d" means that matching - doesn't ever start, and the callout is never reached. However, with + PCRE2 knows that any matching string must contain the letter "d". If + the subject string is "abyz", the lack of "d" means that matching + doesn't ever start, and the callout is never reached. However, with "abyd", though the result is still no match, the callout is obeyed. - For most patterns PCRE2 also knows the minimum length of a matching - string, and will immediately give a "no match" return without actually - running a match if the subject is not long enough, or, for unanchored + For most patterns PCRE2 also knows the minimum length of a matching + string, and will immediately give a "no match" return without actually + running a match if the subject is not long enough, or, for unanchored patterns, if it has been scanned far enough. You can disable these optimizations by passing the PCRE2_NO_START_OPTI- - MIZE option to pcre2_compile(), or by starting the pattern with - (*NO_START_OPT). This slows down the matching process, but does ensure + MIZE option to pcre2_compile(), or by starting the pattern with + (*NO_START_OPT). This slows down the matching process, but does ensure that callouts such as the example above are obeyed. THE CALLOUT INTERFACE - During matching, when PCRE2 reaches a callout point, if an external - function is provided in the match context, it is called. This applies - to both normal, DFA, and JIT matching. The first argument to the call- + During matching, when PCRE2 reaches a callout point, if an external + function is provided in the match context, it is called. This applies + to both normal, DFA, and JIT matching. The first argument to the call- out function is a pointer to a pcre2_callout block. The second argument - is the void * callout data that was supplied when the callout was set + is the void * callout data that was supplied when the callout was set up by calling pcre2_set_callout() (see the pcre2api documentation). The - callout block structure contains the following fields, not necessarily + callout block structure contains the following fields, not necessarily in this order: uint32_t version; @@ -4470,118 +4318,118 @@ THE CALLOUT INTERFACE PCRE2_SIZE callout_string_length; PCRE2_SPTR callout_string; - The version field contains the version number of the block format. The - current version is 2; the three callout string fields were added for - version 1, and the callout_flags field for version 2. If you are writ- - ing an application that might use an earlier release of PCRE2, you - should check the version number before accessing any of these fields. - The version number will increase in future if more fields are added, + The version field contains the version number of the block format. The + current version is 2; the three callout string fields were added for + version 1, and the callout_flags field for version 2. If you are writ- + ing an application that might use an earlier release of PCRE2, you + should check the version number before accessing any of these fields. + The version number will increase in future if more fields are added, but the intention is never to remove any of the existing fields. Fields for numerical callouts - For a numerical callout, callout_string is NULL, and callout_number - contains the number of the callout, in the range 0-255. This is the - number that follows (?C for callouts that part of the pattern; it is + For a numerical callout, callout_string is NULL, and callout_number + contains the number of the callout, in the range 0-255. This is the + number that follows (?C for callouts that part of the pattern; it is 255 for automatically generated callouts. Fields for string callouts - For callouts with string arguments, callout_number is always zero, and - callout_string points to the string that is contained within the com- + For callouts with string arguments, callout_number is always zero, and + callout_string points to the string that is contained within the com- piled pattern. Its length is given by callout_string_length. Duplicated ending delimiters that were present in the original pattern string have been turned into single characters, but there is no other processing of - the callout string argument. An additional code unit containing binary - zero is present after the string, but is not included in the length. - The delimiter that was used to start the string is also stored within - the pattern, immediately before the string itself. You can access this + the callout string argument. An additional code unit containing binary + zero is present after the string, but is not included in the length. + The delimiter that was used to start the string is also stored within + the pattern, immediately before the string itself. You can access this delimiter as callout_string[-1] if you need it. The callout_string_offset field is the code unit offset to the start of the callout argument string within the original pattern string. This is - provided for the benefit of applications such as script languages that + provided for the benefit of applications such as script languages that might need to report errors in the callout string within the pattern. Fields for all callouts - The remaining fields in the callout block are the same for both kinds + The remaining fields in the callout block are the same for both kinds of callout. - The offset_vector field is a pointer to a vector of capturing offsets + The offset_vector field is a pointer to a vector of capturing offsets (the "ovector"). You may read the elements in this vector, but you must not change any of them. - For calls to pcre2_match(), the offset_vector field is not (since - release 10.30) a pointer to the actual ovector that was passed to the - matching function in the match data block. Instead it points to an - internal ovector of a size large enough to hold all possible captured + For calls to pcre2_match(), the offset_vector field is not (since + release 10.30) a pointer to the actual ovector that was passed to the + matching function in the match data block. Instead it points to an + internal ovector of a size large enough to hold all possible captured substrings in the pattern. Note that whenever a recursion or subroutine - call within a pattern completes, the capturing state is reset to what + call within a pattern completes, the capturing state is reset to what it was before. - The capture_last field contains the number of the most recently cap- - tured substring, and the capture_top field contains one more than the - number of the highest numbered captured substring so far. If no sub- - strings have yet been captured, the value of capture_last is 0 and the - value of capture_top is 1. The values of these fields do not always - differ by one; for example, when the callout in the pattern + The capture_last field contains the number of the most recently cap- + tured substring, and the capture_top field contains one more than the + number of the highest numbered captured substring so far. If no sub- + strings have yet been captured, the value of capture_last is 0 and the + value of capture_top is 1. The values of these fields do not always + differ by one; for example, when the callout in the pattern ((a)(b))(?C2) is taken, capture_last is 1 but capture_top is 4. - The contents of ovector[2] to ovector[<capture_top>*2-1] can be + The contents of ovector[2] to ovector[<capture_top>*2-1] can be inspected in order to extract substrings that have been matched so far, - in the same way as extracting substrings after a match has completed. - The values in ovector[0] and ovector[1] are always PCRE2_UNSET because - the match is by definition not complete. Substrings that have not been - captured but whose numbers are less than capture_top also have both of + in the same way as extracting substrings after a match has completed. + The values in ovector[0] and ovector[1] are always PCRE2_UNSET because + the match is by definition not complete. Substrings that have not been + captured but whose numbers are less than capture_top also have both of their ovector slots set to PCRE2_UNSET. - For DFA matching, the offset_vector field points to the ovector that - was passed to the matching function in the match data block for call- + For DFA matching, the offset_vector field points to the ovector that + was passed to the matching function in the match data block for call- outs at the top level, but to an internal ovector during the processing - of pattern recursions, lookarounds, and atomic groups. However, these - ovectors hold no useful information because pcre2_dfa_match() does not - support substring capturing. The value of capture_top is always 1 and + of pattern recursions, lookarounds, and atomic groups. However, these + ovectors hold no useful information because pcre2_dfa_match() does not + support substring capturing. The value of capture_top is always 1 and the value of capture_last is always 0 for DFA matching. The subject and subject_length fields contain copies of the values that were passed to the matching function. - The start_match field normally contains the offset within the subject - at which the current match attempt started. However, if the escape - sequence \K has been encountered, this value is changed to reflect the - modified starting point. If the pattern is not anchored, the callout + The start_match field normally contains the offset within the subject + at which the current match attempt started. However, if the escape + sequence \K has been encountered, this value is changed to reflect the + modified starting point. If the pattern is not anchored, the callout function may be called several times from the same point in the pattern for different starting points in the subject. - The current_position field contains the offset within the subject of + The current_position field contains the offset within the subject of the current match pointer. The pattern_position field contains the offset in the pattern string to the next item to be matched. - The next_item_length field contains the length of the next item to be - processed in the pattern string. When the callout is at the end of the - pattern, the length is zero. When the callout precedes an opening + The next_item_length field contains the length of the next item to be + processed in the pattern string. When the callout is at the end of the + pattern, the length is zero. When the callout precedes an opening parenthesis, the length includes meta characters that follow the paren- - thesis. For example, in a callout before an assertion such as (?=ab) - the length is 3. For an an alternation bar or a closing parenthesis, - the length is one, unless a closing parenthesis is followed by a quan- + thesis. For example, in a callout before an assertion such as (?=ab) + the length is 3. For an an alternation bar or a closing parenthesis, + the length is one, unless a closing parenthesis is followed by a quan- tifier, in which case its length is included. (This changed in release - 10.23. In earlier releases, before an opening parenthesis the length - was that of the entire group, and before an alternation bar or a clos- - ing parenthesis the length was zero.) + 10.23. In earlier releases, before an opening parenthesis the length + was that of the entire subpattern, and before an alternation bar or a + closing parenthesis the length was zero.) - The pattern_position and next_item_length fields are intended to help - in distinguishing between different automatic callouts, which all have - the same callout number. However, they are set for all callouts, and + The pattern_position and next_item_length fields are intended to help + in distinguishing between different automatic callouts, which all have + the same callout number. However, they are set for all callouts, and are used by pcre2test to show the next item to be matched when display- ing callout information. In callouts from pcre2_match() the mark field contains a pointer to the - zero-terminated name of the most recently passed (*MARK), (*PRUNE), or - (*THEN) item in the match, or NULL if no such items have been passed. - Instances of (*PRUNE) or (*THEN) without a name do not obliterate a + zero-terminated name of the most recently passed (*MARK), (*PRUNE), or + (*THEN) item in the match, or NULL if no such items have been passed. + Instances of (*PRUNE) or (*THEN) without a name do not obliterate a previous (*MARK). In callouts from the DFA matching function this field always contains NULL. @@ -4591,25 +4439,25 @@ THE CALLOUT INTERFACE PCRE2_CALLOUT_STARTMATCH - This is set for the first callout after the start of matching for each + This is set for the first callout after the start of matching for each new starting position in the subject. PCRE2_CALLOUT_BACKTRACK - This is set if there has been a matching backtrack since the previous - callout, or since the start of matching if this is the first callout + This is set if there has been a matching backtrack since the previous + callout, or since the start of matching if this is the first callout from a pcre2_match() run. - Both bits are set when a backtrack has caused a "bumpalong" to a new - starting position in the subject. Output from pcre2test does not indi- - cate the presence of these bits unless the callout_extra modifier is + Both bits are set when a backtrack has caused a "bumpalong" to a new + starting position in the subject. Output from pcre2test does not indi- + cate the presence of these bits unless the callout_extra modifier is set. The information in the callout_flags field is provided so that applica- - tions can track and tell their users how matching with backtracking is - done. This can be useful when trying to optimize patterns, or just to - understand how PCRE2 works. There is no support in pcre2_dfa_match() - because there is no backtracking in DFA matching, and there is no sup- + tions can track and tell their users how matching with backtracking is + done. This can be useful when trying to optimize patterns, or just to + understand how PCRE2 works. There is no support in pcre2_dfa_match() + because there is no backtracking in DFA matching, and there is no sup- port in JIT because JIT is all about maximimizing matching performance. In both these cases the callout_flags field is always zero. @@ -4617,16 +4465,16 @@ THE CALLOUT INTERFACE RETURN VALUES FROM CALLOUTS The external callout function returns an integer to PCRE2. If the value - is zero, matching proceeds as normal. If the value is greater than - zero, matching fails at the current point, but the testing of other + is zero, matching proceeds as normal. If the value is greater than + zero, matching fails at the current point, but the testing of other matching possibilities goes ahead, just as if a lookahead assertion had failed. If the value is less than zero, the match is abandoned, and the matching function returns the negative value. - Negative values should normally be chosen from the set of - PCRE2_ERROR_xxx values. In particular, PCRE2_ERROR_NOMATCH forces a - standard "no match" failure. The error number PCRE2_ERROR_CALLOUT is - reserved for use by callout functions; it will never be used by PCRE2 + Negative values should normally be chosen from the set of + PCRE2_ERROR_xxx values. In particular, PCRE2_ERROR_NOMATCH forces a + standard "no match" failure. The error number PCRE2_ERROR_CALLOUT is + reserved for use by callout functions; it will never be used by PCRE2 itself. @@ -4637,14 +4485,14 @@ CALLOUT ENUMERATION void *user_data); A script language that supports the use of string arguments in callouts - might like to scan all the callouts in a pattern before running the + might like to scan all the callouts in a pattern before running the match. This can be done by calling pcre2_callout_enumerate(). The first - argument is a pointer to a compiled pattern, the second points to a - callback function, and the third is arbitrary user data. The callback - function is called for every callout in the pattern in the order in + argument is a pointer to a compiled pattern, the second points to a + callback function, and the third is arbitrary user data. The callback + function is called for every callout in the pattern in the order in which they appear. Its first argument is a pointer to a callout enumer- - ation block, and its second argument is the user_data value that was - passed to pcre2_callout_enumerate(). The data block contains the fol- + ation block, and its second argument is the user_data value that was + passed to pcre2_callout_enumerate(). The data block contains the fol- lowing fields: version Block version number @@ -4655,17 +4503,17 @@ CALLOUT ENUMERATION callout_string_length Length of callout string callout_string Points to callout string or is NULL - The version number is currently 0. It will increase if new fields are - ever added to the block. The remaining fields are the same as their - namesakes in the pcre2_callout block that is used for callouts during + The version number is currently 0. It will increase if new fields are + ever added to the block. The remaining fields are the same as their + namesakes in the pcre2_callout block that is used for callouts during matching, as described above. - Note that the value of pattern_position is unique for each callout. - However, if a callout occurs inside a group that is quantified with a + Note that the value of pattern_position is unique for each callout. + However, if a callout occurs inside a group that is quantified with a non-zero minimum or a fixed maximum, the group is replicated inside the - compiled pattern. For example, a pattern such as /(a){2}/ is compiled - as if it were /(a)(a)/. This means that the callout will be enumerated - more than once, but with the same value for pattern_position in each + compiled pattern. For example, a pattern such as /(a){2}/ is compiled + as if it were /(a)(a)/. This means that the callout will be enumerated + more than once, but with the same value for pattern_position in each case. The callback function should normally return zero. If it returns a non- @@ -4682,8 +4530,8 @@ AUTHOR REVISION - Last updated: 03 February 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 26 April 2018 + Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ @@ -4712,10 +4560,10 @@ DIFFERENCES BETWEEN PCRE2 AND PERL repeat quantifiers on other assertions, for example, \b* (but not \b{3}), but these do not seem to have any use. - 3. Capture groups that occur inside negative lookaround assertions are - counted, but their entries in the offsets vector are set only when a - negative assertion is a condition that has a matching branch (that is, - the condition is false). + 3. Capturing subpatterns that occur inside negative lookaround asser- + tions are counted, but their entries in the offsets vector are set only + when a negative assertion is a condition that has a matching branch + (that is, the condition is false). 4. The following Perl escape sequences are not supported: \F, \l, \L, \u, \U, and \N when followed by a character name. \N on its own, match- @@ -4723,28 +4571,27 @@ DIFFERENCES BETWEEN PCRE2 AND PERL point, are supported. The escapes that modify the case of following letters are implemented by Perl's general string-handling and are not part of its pattern matching engine. If any of these are encountered by - PCRE2, an error is generated by default. However, if either of the - PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX options is set, \U and \u are - interpreted as ECMAScript interprets them. + PCRE2, an error is generated by default. However, if the PCRE2_ALT_BSUX + option is set, \U and \u are interpreted as ECMAScript interprets them. 5. The Perl escape sequences \p, \P, and \X are supported only if PCRE2 is built with Unicode support (the default). The properties that can be - tested with \p and \P are limited to the general category properties - such as Lu and Nd, script names such as Greek or Han, and the derived + tested with \p and \P are limited to the general category properties + such as Lu and Nd, script names such as Greek or Han, and the derived properties Any and L&. PCRE2 does support the Cs (surrogate) property, - which Perl does not; the Perl documentation says "Because Perl hides + which Perl does not; the Perl documentation says "Because Perl hides the need for the user to understand the internal representation of Uni- - code characters, there is no need to implement the somewhat messy con- + code characters, there is no need to implement the somewhat messy con- cept of surrogates." 6. PCRE2 supports the \Q...\E escape for quoting substrings. Characters in between are treated as literals. However, this is slightly different - from Perl in that $ and @ are also handled as literals inside the + from Perl in that $ and @ are also handled as literals inside the quotes. In Perl, they cause variable interpolation (but of course PCRE2 - does not have variables). Also, Perl does "double-quotish backslash + does not have variables). Also, Perl does "double-quotish backslash interpolation" on any backslashes between \Q and \E which, its documen- - tation says, "may lead to confusing results". PCRE2 treats a backslash - between \Q and \E just like any other character. Note the following + tation says, "may lead to confusing results". PCRE2 treats a backslash + between \Q and \E just like any other character. Note the following examples: Pattern PCRE2 matches Perl matches @@ -4756,54 +4603,55 @@ DIFFERENCES BETWEEN PCRE2 AND PERL \QA\B\E A\B A\B \Q\\E \ \\E - The \Q...\E sequence is recognized both inside and outside character + The \Q...\E sequence is recognized both inside and outside character classes. - 7. Fairly obviously, PCRE2 does not support the (?{code}) and + 7. Fairly obviously, PCRE2 does not support the (?{code}) and (??{code}) constructions. However, PCRE2 does have a "callout" feature, which allows an external function to be called during pattern matching. See the pcre2callout documentation for details. - 8. Subroutine calls (whether recursive or not) were treated as atomic - groups up to PCRE2 release 10.23, but from release 10.30 this changed, + 8. Subroutine calls (whether recursive or not) were treated as atomic + groups up to PCRE2 release 10.23, but from release 10.30 this changed, and backtracking into subroutine calls is now supported, as in Perl. - 9. If any of the backtracking control verbs are used in a group that is - called as a subroutine (whether or not recursively), their effect is - confined to that group; it does not extend to the surrounding pattern. - This is not always the case in Perl. In particular, if (*THEN) is - present in a group that is called as a subroutine, its action is lim- - ited to that group, even if the group does not contain any | charac- - ters. Note that such groups are processed as anchored at the point - where they are tested. - - 10. If a pattern contains more than one backtracking control verb, the - first one that is backtracked onto acts. For example, in the pattern - A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure + 9. If any of the backtracking control verbs are used in a subpattern + that is called as a subroutine (whether or not recursively), their + effect is confined to that subpattern; it does not extend to the sur- + rounding pattern. This is not always the case in Perl. In particular, + if (*THEN) is present in a group that is called as a subroutine, its + action is limited to that group, even if the group does not contain any + | characters. Note that such subpatterns are processed as anchored at + the point where they are tested. + + 10. If a pattern contains more than one backtracking control verb, the + first one that is backtracked onto acts. For example, in the pattern + A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases it is the same as PCRE2, but there are cases where it differs. - 11. Most backtracking verbs in assertions have their normal actions. + 11. Most backtracking verbs in assertions have their normal actions. They are not confined to the assertion. - 12. There are some differences that are concerned with the settings of - captured strings when part of a pattern is repeated. For example, - matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 + 12. There are some differences that are concerned with the settings of + captured strings when part of a pattern is repeated. For example, + matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 unset, but in PCRE2 it is set to "b". - 13. PCRE2's handling of duplicate capture group numbers and names is - not as general as Perl's. This is a consequence of the fact the PCRE2 - works internally just with numbers, using an external table to trans- - late between numbers and names. In particular, a pattern such as - (?|(?<a>A)|(?<b>B), where the two capture groups have the same number - but different names, is not supported, and causes an error at compile - time. If it were allowed, it would not be possible to distinguish which - group matched, because both names map to capture group number 1. To - avoid this confusing situation, an error is given at compile time. + 13. PCRE2's handling of duplicate subpattern numbers and duplicate sub- + pattern names is not as general as Perl's. This is a consequence of the + fact the PCRE2 works internally just with numbers, using an external + table to translate between numbers and names. In particular, a pattern + such as (?|(?<a>A)|(?<b>B), where the two capturing parentheses have + the same number but different names, is not supported, and causes an + error at compile time. If it were allowed, it would not be possible to + distinguish which parentheses matched, because both names map to cap- + turing subpattern number 1. To avoid this confusing situation, an error + is given at compile time. 14. Perl used to recognize comments in some places that PCRE2 does not, - for example, between the ( and ? at the start of a group. If the /x - modifier is set, Perl allowed white space between ( and ? though the + for example, between the ( and ? at the start of a subpattern. If the + /x modifier is set, Perl allowed white space between ( and ? though the latest Perls give an error (for a while it was just deprecated). There may still be some cases where Perl behaves differently. @@ -4887,8 +4735,8 @@ AUTHOR REVISION - Last updated: 12 February 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 28 July 2018 + Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ @@ -5010,56 +4858,32 @@ SIMPLE USE OF JIT to handle the pattern. -MATCHING SUBJECTS CONTAINING INVALID UTF - - When a pattern is compiled with the PCRE2_UTF option, the interpretive - matching function expects its subject string to be a valid sequence of - UTF code units. If it is not, the result is undefined. This is also - true by default of matching via JIT. However, if the option - PCRE2_JIT_INVALID_UTF is passed to pcre2_jit_compile(), code that can - process a subject containing invalid UTF is compiled. - - In this mode, an invalid code unit sequence never matches any pattern - item. It does not match dot, it does not match \p{Any}, it does not - even match negative items such as [^X]. A lookbehind assertion fails if - it encounters an invalid sequence while moving the current point back- - wards. In other words, an invalid UTF code unit sequence acts as a bar- - rier which no match can cross. Reaching an invalid sequence causes an - immediate backtrack. - - Using this option, an application can run matches in arbitrary data, - knowing that any matched strings that are returned will be valid UTF. - This can be useful when searching for text in executable or other - binary files. - - UNSUPPORTED OPTIONS AND PATTERN ITEMS The pcre2_match() options that are supported for JIT matching are - PCRE2_COPY_MATCHED_SUBJECT, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, - PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and - PCRE2_PARTIAL_SOFT. The PCRE2_ANCHORED and PCRE2_ENDANCHORED options - are not supported at match time. + PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART, + PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. The + PCRE2_ANCHORED option is not supported at match time. - If the PCRE2_NO_JIT option is passed to pcre2_match() it disables the + If the PCRE2_NO_JIT option is passed to pcre2_match() it disables the use of JIT, forcing matching by the interpreter code. - The only unsupported pattern items are \C (match a single data unit) - when running in a UTF mode, and a callout immediately before an asser- + The only unsupported pattern items are \C (match a single data unit) + when running in a UTF mode, and a callout immediately before an asser- tion condition in a conditional group. RETURN VALUES FROM JIT MATCHING When a pattern is matched using JIT matching, the return values are the - same as those given by the interpretive pcre2_match() code, with the - addition of one new error code: PCRE2_ERROR_JIT_STACKLIMIT. This means - that the memory used for the JIT stack was insufficient. See "Control- + same as those given by the interpretive pcre2_match() code, with the + addition of one new error code: PCRE2_ERROR_JIT_STACKLIMIT. This means + that the memory used for the JIT stack was insufficient. See "Control- ling the JIT stack" below for a discussion of JIT stack usage. - The error code PCRE2_ERROR_MATCHLIMIT is returned by the JIT code if - searching a very large pattern tree goes on for too long, as it is in - the same circumstance when JIT is not used, but the details of exactly + The error code PCRE2_ERROR_MATCHLIMIT is returned by the JIT code if + searching a very large pattern tree goes on for too long, as it is in + the same circumstance when JIT is not used, but the details of exactly what is counted are not the same. The PCRE2_ERROR_DEPTHLIMIT error code is never returned when JIT matching is used. @@ -5067,25 +4891,25 @@ RETURN VALUES FROM JIT MATCHING CONTROLLING THE JIT STACK When the compiled JIT code runs, it needs a block of memory to use as a - stack. By default, it uses 32KiB on the machine stack. However, some - large or complicated patterns need more than this. The error - PCRE2_ERROR_JIT_STACKLIMIT is given when there is not enough stack. - Three functions are provided for managing blocks of memory for use as - JIT stacks. There is further discussion about the use of JIT stacks in + stack. By default, it uses 32KiB on the machine stack. However, some + large or complicated patterns need more than this. The error + PCRE2_ERROR_JIT_STACKLIMIT is given when there is not enough stack. + Three functions are provided for managing blocks of memory for use as + JIT stacks. There is further discussion about the use of JIT stacks in the section entitled "JIT stack FAQ" below. - The pcre2_jit_stack_create() function creates a JIT stack. Its argu- - ments are a starting size, a maximum size, and a general context (for - memory allocation functions, or NULL for standard memory allocation). + The pcre2_jit_stack_create() function creates a JIT stack. Its argu- + ments are a starting size, a maximum size, and a general context (for + memory allocation functions, or NULL for standard memory allocation). It returns a pointer to an opaque structure of type pcre2_jit_stack, or - NULL if there is an error. The pcre2_jit_stack_free() function is used + NULL if there is an error. The pcre2_jit_stack_free() function is used to free a stack that is no longer needed. If its argument is NULL, this - function returns immediately, without doing anything. (For the techni- - cally minded: the address space is allocated by mmap or VirtualAlloc.) - A maximum stack size of 512KiB to 1MiB should be more than enough for + function returns immediately, without doing anything. (For the techni- + cally minded: the address space is allocated by mmap or VirtualAlloc.) + A maximum stack size of 512KiB to 1MiB should be more than enough for any pattern. - The pcre2_jit_stack_assign() function specifies which stack JIT code + The pcre2_jit_stack_assign() function specifies which stack JIT code should use. Its arguments are as follows: pcre2_match_context *mcontext @@ -5095,7 +4919,7 @@ CONTROLLING THE JIT STACK The first argument is a pointer to a match context. When this is subse- quently passed to a matching function, its information determines which JIT stack is used. If this argument is NULL, the function returns imme- - diately, without doing anything. There are three cases for the values + diately, without doing anything. There are three cases for the values of the other two options: (1) If callback is NULL and data is NULL, an internal 32KiB block @@ -5113,34 +4937,34 @@ CONTROLLING THE JIT STACK return value must be a valid JIT stack, the result of calling pcre2_jit_stack_create(). - A callback function is obeyed whenever JIT code is about to be run; it + A callback function is obeyed whenever JIT code is about to be run; it is not obeyed when pcre2_match() is called with options that are incom- - patible for JIT matching. A callback function can therefore be used to - determine whether a match operation was executed by JIT or by the + patible for JIT matching. A callback function can therefore be used to + determine whether a match operation was executed by JIT or by the interpreter. You may safely use the same JIT stack for more than one pattern (either - by assigning directly or by callback), as long as the patterns are + by assigning directly or by callback), as long as the patterns are matched sequentially in the same thread. Currently, the only way to set - up non-sequential matches in one thread is to use callouts: if a call- - out function starts another match, that match must use a different JIT + up non-sequential matches in one thread is to use callouts: if a call- + out function starts another match, that match must use a different JIT stack to the one used for currently suspended match(es). - In a multithread application, if you do not specify a JIT stack, or if - you assign or pass back NULL from a callback, that is thread-safe, - because each thread has its own machine stack. However, if you assign - or pass back a non-NULL JIT stack, this must be a different stack for + In a multithread application, if you do not specify a JIT stack, or if + you assign or pass back NULL from a callback, that is thread-safe, + because each thread has its own machine stack. However, if you assign + or pass back a non-NULL JIT stack, this must be a different stack for each thread so that the application is thread-safe. - Strictly speaking, even more is allowed. You can assign the same non- - NULL stack to a match context that is used by any number of patterns, - as long as they are not used for matching by multiple threads at the - same time. For example, you could use the same stack in all compiled - patterns, with a global mutex in the callback to wait until the stack + Strictly speaking, even more is allowed. You can assign the same non- + NULL stack to a match context that is used by any number of patterns, + as long as they are not used for matching by multiple threads at the + same time. For example, you could use the same stack in all compiled + patterns, with a global mutex in the callback to wait until the stack is available for use. However, this is an inefficient solution, and not recommended. - This is a suggestion for how a multithreaded program that needs to set + This is a suggestion for how a multithreaded program that needs to set up non-default JIT stacks might operate: During thread initalization @@ -5152,7 +4976,7 @@ CONTROLLING THE JIT STACK Use a one-line callback function return thread_local_var - All the functions described in this section do nothing if JIT is not + All the functions described in this section do nothing if JIT is not available. @@ -5161,20 +4985,20 @@ JIT STACK FAQ (1) Why do we need JIT stacks? PCRE2 (and JIT) is a recursive, depth-first engine, so it needs a stack - where the local data of the current node is pushed before checking its + where the local data of the current node is pushed before checking its child nodes. Allocating real machine stack on some platforms is diffi- cult. For example, the stack chain needs to be updated every time if we - extend the stack on PowerPC. Although it is possible, its updating + extend the stack on PowerPC. Although it is possible, its updating time overhead decreases performance. So we do the recursion in memory. (2) Why don't we simply allocate blocks of memory with malloc()? - Modern operating systems have a nice feature: they can reserve an + Modern operating systems have a nice feature: they can reserve an address space instead of allocating memory. We can safely allocate mem- - ory pages inside this address space, so the stack could grow without + ory pages inside this address space, so the stack could grow without moving memory data (this is important because of pointers). Thus we can allocate 1MiB address space, and use only a single memory page (usually - 4KiB) if that is enough. However, we can still grow up to 1MiB anytime + 4KiB) if that is enough. However, we can still grow up to 1MiB anytime if needed. (3) Who "owns" a JIT stack? @@ -5182,8 +5006,8 @@ JIT STACK FAQ The owner of the stack is the user program, not the JIT studied pattern or anything else. The user program must ensure that if a stack is being used by pcre2_match(), (that is, it is assigned to a match context that - is passed to the pattern currently running), that stack must not be - used by any other threads (to avoid overwriting the same memory area). + is passed to the pattern currently running), that stack must not be + used by any other threads (to avoid overwriting the same memory area). The best practice for multithreaded programs is to allocate a stack for each thread, and return this stack through the JIT callback function. @@ -5191,36 +5015,36 @@ JIT STACK FAQ You can free a JIT stack at any time, as long as it will not be used by pcre2_match() again. When you assign the stack to a match context, only - a pointer is set. There is no reference counting or any other magic. + a pointer is set. There is no reference counting or any other magic. You can free compiled patterns, contexts, and stacks in any order, any- - time. Just do not call pcre2_match() with a match context pointing to + time. Just do not call pcre2_match() with a match context pointing to an already freed stack, as that will cause SEGFAULT. (Also, do not free - a stack currently used by pcre2_match() in another thread). You can - also replace the stack in a context at any time when it is not in use. + a stack currently used by pcre2_match() in another thread). You can + also replace the stack in a context at any time when it is not in use. You should free the previous stack before assigning a replacement. - (5) Should I allocate/free a stack every time before/after calling + (5) Should I allocate/free a stack every time before/after calling pcre2_match()? - No, because this is too costly in terms of resources. However, you - could implement some clever idea which release the stack if it is not - used in let's say two minutes. The JIT callback can help to achieve + No, because this is too costly in terms of resources. However, you + could implement some clever idea which release the stack if it is not + used in let's say two minutes. The JIT callback can help to achieve this without keeping a list of patterns. - (6) OK, the stack is for long term memory allocation. But what happens - if a pattern causes stack overflow with a stack of 1MiB? Is that 1MiB + (6) OK, the stack is for long term memory allocation. But what happens + if a pattern causes stack overflow with a stack of 1MiB? Is that 1MiB kept until the stack is freed? - Especially on embedded sytems, it might be a good idea to release mem- - ory sometimes without freeing the stack. There is no API for this at - the moment. Probably a function call which returns with the currently - allocated memory for any stack and another which allows releasing mem- + Especially on embedded sytems, it might be a good idea to release mem- + ory sometimes without freeing the stack. There is no API for this at + the moment. Probably a function call which returns with the currently + allocated memory for any stack and another which allows releasing mem- ory (shrinking the stack) would be a good idea if someone needs this. (7) This is too much of a headache. Isn't there any better solution for JIT stack handling? - No, thanks to Windows. If POSIX threads were used everywhere, we could + No, thanks to Windows. If POSIX threads were used everywhere, we could throw out this complicated API. @@ -5229,18 +5053,18 @@ FREEING JIT SPECULATIVE MEMORY void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext); The JIT executable allocator does not free all memory when it is possi- - ble. It expects new allocations, and keeps some free memory around to - improve allocation speed. However, in low memory conditions, it might - be better to free all possible memory. You can cause this to happen by - calling pcre2_jit_free_unused_memory(). Its argument is a general con- + ble. It expects new allocations, and keeps some free memory around to + improve allocation speed. However, in low memory conditions, it might + be better to free all possible memory. You can cause this to happen by + calling pcre2_jit_free_unused_memory(). Its argument is a general con- text, for custom memory management, or NULL for standard memory manage- ment. EXAMPLE CODE - This is a single-threaded example that specifies a JIT stack without - using a callback. A real program should include error checking after + This is a single-threaded example that specifies a JIT stack without + using a callback. A real program should include error checking after all the function calls. int rc; @@ -5268,31 +5092,29 @@ EXAMPLE CODE JIT FAST PATH API Because the API described above falls back to interpreted matching when - JIT is not available, it is convenient for programs that are written + JIT is not available, it is convenient for programs that are written for general use in many environments. However, calling JIT via pcre2_match() does have a performance impact. Programs that are written - for use where JIT is known to be available, and which need the best - possible performance, can instead use a "fast path" API to call JIT - matching directly instead of calling pcre2_match() (obviously only for + for use where JIT is known to be available, and which need the best + possible performance, can instead use a "fast path" API to call JIT + matching directly instead of calling pcre2_match() (obviously only for patterns that have been successfully processed by pcre2_jit_compile()). - The fast path function is called pcre2_jit_match(), and it takes - exactly the same arguments as pcre2_match(). However, the subject - string must be specified with a length; PCRE2_ZERO_TERMINATED is not - supported. Unsupported option bits (for example, PCRE2_ANCHORED, - PCRE2_ENDANCHORED and PCRE2_COPY_MATCHED_SUBJECT) are ignored, as is - the PCRE2_NO_JIT option. The return values are also the same as for - pcre2_match(), plus PCRE2_ERROR_JIT_BADOPTION if a matching mode (par- - tial or complete) is requested that was not compiled. + The fast path function is called pcre2_jit_match(), and it takes + exactly the same arguments as pcre2_match(). The return values are also + the same, plus PCRE2_ERROR_JIT_BADOPTION if a matching mode (partial or + complete) is requested that was not compiled. Unsupported option bits + (for example, PCRE2_ANCHORED) are ignored, as is the PCRE2_NO_JIT + option. - When you call pcre2_match(), as well as testing for invalid options, a + When you call pcre2_match(), as well as testing for invalid options, a number of other sanity checks are performed on the arguments. For exam- ple, if the subject pointer is NULL, an immediate error is given. Also, - unless PCRE2_NO_UTF_CHECK is set, a UTF subject string is tested for - validity. In the interests of speed, these checks do not happen on the + unless PCRE2_NO_UTF_CHECK is set, a UTF subject string is tested for + validity. In the interests of speed, these checks do not happen on the JIT fast path, and if invalid data is passed, the result is undefined. - Bypassing the sanity checks and the pcre2_match() wrapping can give + Bypassing the sanity checks and the pcre2_match() wrapping can give speedups of more than 10%. @@ -5310,8 +5132,8 @@ AUTHOR REVISION - Last updated: 06 March 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 28 June 2018 + Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ @@ -5352,22 +5174,23 @@ SIZE AND OTHER LIMITATIONS The maximum length of a lookbehind assertion is 65535 characters. - There is no limit to the number of parenthesized groups, but there can - be no more than 65535 capture groups, and there is a limit to the depth - of nesting of parenthesized subpatterns of all kinds. This is imposed - in order to limit the amount of system stack used at compile time. The - default limit can be specified when PCRE2 is built; if not, the default - is set to 250. An application can change this limit by calling - pcre2_set_parens_nest_limit() to set the limit in a compile context. + There is no limit to the number of parenthesized subpatterns, but there + can be no more than 65535 capturing subpatterns. There is, however, a + limit to the depth of nesting of parenthesized subpatterns of all + kinds. This is imposed in order to limit the amount of system stack + used at compile time. The default limit can be specified when PCRE2 is + built; if not, the default is set to 250. An application can change + this limit by calling pcre2_set_parens_nest_limit() to set the limit in + a compile context. - The maximum length of name for a named capture group is 32 code units, - and the maximum number of such groups is 10000. + The maximum length of name for a named subpattern is 32 code units, and + the maximum number of named subpatterns is 10000. - The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or - (*THEN) verb is 255 code units for the 8-bit library and 65535 code + The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or + (*THEN) verb is 255 code units for the 8-bit library and 65535 code units for the 16-bit and 32-bit libraries. - The maximum length of a string argument to a callout is the largest + The maximum length of a string argument to a callout is the largest number a 32-bit unsigned integer can hold. @@ -5380,8 +5203,8 @@ AUTHOR REVISION - Last updated: 02 February 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 30 March 2017 + Copyright (c) 1997-2017 University of Cambridge. ------------------------------------------------------------------------------ @@ -5505,8 +5328,8 @@ THE ALTERNATIVE MATCHING ALGORITHM SESS option when compiling. There are a number of features of PCRE2 regular expressions that are - not supported or behave differently in the alternative matching func- - tion. Those that are not supported cause an error if encountered. + not supported by the alternative matching algorithm. They are as fol- + lows: 1. Because the algorithm finds all possible matches, the greedy or ungreedy nature of repetition quantifiers is not relevant (though it @@ -5531,48 +5354,47 @@ THE ALTERNATIVE MATCHING ALGORITHM strings are available. 3. Because no substrings are captured, backreferences within the pat- - tern are not supported. + tern are not supported, and cause errors if encountered. 4. For the same reason, conditional expressions that use a backrefer- ence as the condition or test for a specific group recursion are not supported. - 5. Again for the same reason, script runs are not supported. - - 6. Because many paths through the tree may be active, the \K escape + 5. Because many paths through the tree may be active, the \K escape sequence, which resets the start of the match when encountered (but may - be on some paths and not on others), is not supported. + be on some paths and not on others), is not supported. It causes an + error if encountered. - 7. Callouts are supported, but the value of the capture_top field is + 6. Callouts are supported, but the value of the capture_top field is always 1, and the value of the capture_last field is always 0. - 8. The \C escape sequence, which (in the standard algorithm) always - matches a single code unit, even in a UTF mode, is not supported in - these modes, because the alternative algorithm moves through the sub- - ject string one character (not code unit) at a time, for all active + 7. The \C escape sequence, which (in the standard algorithm) always + matches a single code unit, even in a UTF mode, is not supported in + these modes, because the alternative algorithm moves through the sub- + ject string one character (not code unit) at a time, for all active paths through the tree. - 9. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) - are not supported. (*FAIL) is supported, and behaves like a failing + 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) + are not supported. (*FAIL) is supported, and behaves like a failing negative assertion. ADVANTAGES OF THE ALTERNATIVE ALGORITHM - Using the alternative matching algorithm provides the following advan- + Using the alternative matching algorithm provides the following advan- tages: 1. All possible matches (at a single point in the subject) are automat- - ically found, and in particular, the longest match is found. To find + ically found, and in particular, the longest match is found. To find more than one match using the standard algorithm, you have to do kludgy things with callouts. - 2. Because the alternative algorithm scans the subject string just + 2. Because the alternative algorithm scans the subject string just once, and never needs to backtrack (except for lookbehinds), it is pos- - sible to pass very long subject strings to the matching function in + sible to pass very long subject strings to the matching function in several pieces, checking for partial matching each time. Although it is - also possible to do multi-segment matching using the standard algo- - rithm, by retaining partially matched substrings, it is more compli- + also possible to do multi-segment matching using the standard algo- + rithm, by retaining partially matched substrings, it is more compli- cated. The pcre2partial documentation gives details of partial matching and discusses multi-segment matching. @@ -5581,12 +5403,11 @@ DISADVANTAGES OF THE ALTERNATIVE ALGORITHM The alternative algorithm suffers from a number of disadvantages: - 1. It is substantially slower than the standard algorithm. This is - partly because it has to search for all possible matches, but is also + 1. It is substantially slower than the standard algorithm. This is + partly because it has to search for all possible matches, but is also because it is less susceptible to optimization. - 2. Capturing parentheses, backreferences, and script runs are not sup- - ported. + 2. Capturing parentheses and backreferences are not supported. 3. Although atomic groups are supported, their use does not provide the performance advantage that it does for the standard algorithm. @@ -5601,8 +5422,8 @@ AUTHOR REVISION - Last updated: 10 October 2018 - Copyright (c) 1997-2018 University of Cambridge. + Last updated: 29 September 2014 + Copyright (c) 1997-2014 University of Cambridge. ------------------------------------------------------------------------------ @@ -6070,23 +5891,22 @@ PCRE2 REGULAR EXPRESSION DETAILS great detail. This description of PCRE2's regular expressions is intended as reference material. - This document discusses the regular expression patterns that are sup- - ported by PCRE2 when its main matching function, pcre2_match(), is - used. PCRE2 also has an alternative matching function, - pcre2_dfa_match(), which matches using a different algorithm that is - not Perl-compatible. Some of the features discussed below are not - available when DFA matching is used. The advantages and disadvantages - of the alternative function, and how it differs from the normal func- - tion, are discussed in the pcre2matching page. + This document discusses the patterns that are supported by PCRE2 when + its main matching function, pcre2_match(), is used. PCRE2 also has an + alternative matching function, pcre2_dfa_match(), which matches using a + different algorithm that is not Perl-compatible. Some of the features + discussed below are not available when DFA matching is used. The advan- + tages and disadvantages of the alternative function, and how it differs + from the normal function, are discussed in the pcre2matching page. SPECIAL START-OF-PATTERN ITEMS - A number of options that can be passed to pcre2_compile() can also be + A number of options that can be passed to pcre2_compile() can also be set by special items at the start of a pattern. These are not Perl-com- - patible, but are provided to make these options accessible to pattern - writers who are not able to change the program that processes the pat- - tern. Any number of these items may appear, but they must all be + patible, but are provided to make these options accessible to pattern + writers who are not able to change the program that processes the pat- + tern. Any number of these items may appear, but they must all be together right at the start of the pattern string, and the letters must be in upper case. @@ -6094,86 +5914,86 @@ SPECIAL START-OF-PATTERN ITEMS In the 8-bit and 16-bit PCRE2 libraries, characters may be coded either as single code units, or as multiple UTF-8 or UTF-16 code units. UTF-32 - can be specified for the 32-bit library, in which case it constrains - the character values to valid Unicode code points. To process UTF - strings, PCRE2 must be built to include Unicode support (which is the - default). When using UTF strings you must either call the compiling - function with the PCRE2_UTF option, or the pattern must start with the - special sequence (*UTF), which is equivalent to setting the relevant + can be specified for the 32-bit library, in which case it constrains + the character values to valid Unicode code points. To process UTF + strings, PCRE2 must be built to include Unicode support (which is the + default). When using UTF strings you must either call the compiling + function with the PCRE2_UTF option, or the pattern must start with the + special sequence (*UTF), which is equivalent to setting the relevant option. How setting a UTF mode affects pattern matching is mentioned in - several places below. There is also a summary of features in the + several places below. There is also a summary of features in the pcre2unicode page. Some applications that allow their users to supply patterns may wish to - restrict them to non-UTF data for security reasons. If the - PCRE2_NEVER_UTF option is passed to pcre2_compile(), (*UTF) is not + restrict them to non-UTF data for security reasons. If the + PCRE2_NEVER_UTF option is passed to pcre2_compile(), (*UTF) is not allowed, and its appearance in a pattern causes an error. Unicode property support - Another special sequence that may appear at the start of a pattern is - (*UCP). This has the same effect as setting the PCRE2_UCP option: it - causes sequences such as \d and \w to use Unicode properties to deter- + Another special sequence that may appear at the start of a pattern is + (*UCP). This has the same effect as setting the PCRE2_UCP option: it + causes sequences such as \d and \w to use Unicode properties to deter- mine character types, instead of recognizing only characters with codes less than 256 via a lookup table. Some applications that allow their users to supply patterns may wish to - restrict them for security reasons. If the PCRE2_NEVER_UCP option is + restrict them for security reasons. If the PCRE2_NEVER_UCP option is passed to pcre2_compile(), (*UCP) is not allowed, and its appearance in a pattern causes an error. Locking out empty string matching Starting a pattern with (*NOTEMPTY) or (*NOTEMPTY_ATSTART) has the same - effect as passing the PCRE2_NOTEMPTY or PCRE2_NOTEMPTY_ATSTART option + effect as passing the PCRE2_NOTEMPTY or PCRE2_NOTEMPTY_ATSTART option to whichever matching function is subsequently called to match the pat- - tern. These options lock out the matching of empty strings, either + tern. These options lock out the matching of empty strings, either entirely, or only at the start of the subject. Disabling auto-possessification - If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as - setting the PCRE2_NO_AUTO_POSSESS option. This stops PCRE2 from making - quantifiers possessive when what follows cannot match the repeated + If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as + setting the PCRE2_NO_AUTO_POSSESS option. This stops PCRE2 from making + quantifiers possessive when what follows cannot match the repeated item. For example, by default a+b is treated as a++b. For more details, see the pcre2api documentation. Disabling start-up optimizations - If a pattern starts with (*NO_START_OPT), it has the same effect as + If a pattern starts with (*NO_START_OPT), it has the same effect as setting the PCRE2_NO_START_OPTIMIZE option. This disables several opti- - mizations for quickly reaching "no match" results. For more details, + mizations for quickly reaching "no match" results. For more details, see the pcre2api documentation. Disabling automatic anchoring - If a pattern starts with (*NO_DOTSTAR_ANCHOR), it has the same effect - as setting the PCRE2_NO_DOTSTAR_ANCHOR option. This disables optimiza- + If a pattern starts with (*NO_DOTSTAR_ANCHOR), it has the same effect + as setting the PCRE2_NO_DOTSTAR_ANCHOR option. This disables optimiza- tions that apply to patterns whose top-level branches all start with .* - (match any number of arbitrary characters). For more details, see the + (match any number of arbitrary characters). For more details, see the pcre2api documentation. Disabling JIT compilation - If a pattern that starts with (*NO_JIT) is successfully compiled, an - attempt by the application to apply the JIT optimization by calling + If a pattern that starts with (*NO_JIT) is successfully compiled, an + attempt by the application to apply the JIT optimization by calling pcre2_jit_compile() is ignored. Setting match resource limits The pcre2_match() function contains a counter that is incremented every time it goes round its main loop. The caller of pcre2_match() can set a - limit on this counter, which therefore limits the amount of computing + limit on this counter, which therefore limits the amount of computing resource used for a match. The maximum depth of nested backtracking can - also be limited; this indirectly restricts the amount of heap memory - that is used, but there is also an explicit memory limit that can be + also be limited; this indirectly restricts the amount of heap memory + that is used, but there is also an explicit memory limit that can be set. - These facilities are provided to catch runaway matches that are pro- - voked by patterns with huge matching trees. A common example is a pat- - tern with nested unlimited repeats applied to a long string that does - not match. When one of these limits is reached, pcre2_match() gives an - error return. The limits can also be set by items at the start of the + These facilities are provided to catch runaway matches that are pro- + voked by patterns with huge matching trees (a typical example is a pat- + tern with nested unlimited repeats applied to a long string that does + not match). When one of these limits is reached, pcre2_match() gives an + error return. The limits can also be set by items at the start of the pattern of the form (*LIMIT_HEAP=d) @@ -6181,35 +6001,35 @@ SPECIAL START-OF-PATTERN ITEMS (*LIMIT_DEPTH=d) where d is any number of decimal digits. However, the value of the set- - ting must be less than the value set (or defaulted) by the caller of - pcre2_match() for it to have any effect. In other words, the pattern - writer can lower the limits set by the programmer, but not raise them. - If there is more than one setting of one of these limits, the lower - value is used. The heap limit is specified in kibibytes (units of 1024 + ting must be less than the value set (or defaulted) by the caller of + pcre2_match() for it to have any effect. In other words, the pattern + writer can lower the limits set by the programmer, but not raise them. + If there is more than one setting of one of these limits, the lower + value is used. The heap limit is specified in kibibytes (units of 1024 bytes). - Prior to release 10.30, LIMIT_DEPTH was called LIMIT_RECURSION. This + Prior to release 10.30, LIMIT_DEPTH was called LIMIT_RECURSION. This name is still recognized for backwards compatibility. The heap limit applies only when the pcre2_match() or pcre2_dfa_match() interpreters are used for matching. It does not apply to JIT. The match - limit is used (but in a different way) when JIT is being used, or when + limit is used (but in a different way) when JIT is being used, or when pcre2_dfa_match() is called, to limit computing resource usage by those - matching functions. The depth limit is ignored by JIT but is relevant - for DFA matching, which uses function recursion for recursions within - the pattern and for lookaround assertions and atomic groups. In this + matching functions. The depth limit is ignored by JIT but is relevant + for DFA matching, which uses function recursion for recursions within + the pattern and for lookaround assertions and atomic groups. In this case, the depth limit controls the depth of such recursion. Newline conventions - PCRE2 supports six different conventions for indicating line breaks in - strings: a single CR (carriage return) character, a single LF (line- + PCRE2 supports six different conventions for indicating line breaks in + strings: a single CR (carriage return) character, a single LF (line- feed) character, the two-character sequence CRLF, any of the three pre- - ceding, any Unicode newline sequence, or the NUL character (binary - zero). The pcre2api page has further discussion about newlines, and + ceding, any Unicode newline sequence, or the NUL character (binary + zero). The pcre2api page has further discussion about newlines, and shows how to set the newline convention when calling pcre2_compile(). - It is also possible to specify a newline convention by starting a pat- + It is also possible to specify a newline convention by starting a pat- tern string with one of the following sequences: (*CR) carriage return @@ -6220,7 +6040,7 @@ SPECIAL START-OF-PATTERN ITEMS (*NUL) the NUL character (binary zero) These override the default and the options given to the compiling func- - tion. For example, on a Unix system where LF is the default newline + tion. For example, on a Unix system where LF is the default newline sequence, the pattern (*CR)a.b @@ -6229,39 +6049,39 @@ SPECIAL START-OF-PATTERN ITEMS no longer a newline. If more than one of these settings is present, the last one is used. - The newline convention affects where the circumflex and dollar asser- + The newline convention affects where the circumflex and dollar asser- tions are true. It also affects the interpretation of the dot metachar- - acter when PCRE2_DOTALL is not set, and the behaviour of \N when not - followed by an opening brace. However, it does not affect what the \R - escape sequence matches. By default, this is any Unicode newline + acter when PCRE2_DOTALL is not set, and the behaviour of \N when not + followed by an opening brace. However, it does not affect what the \R + escape sequence matches. By default, this is any Unicode newline sequence, for Perl compatibility. However, this can be changed; see the next section and the description of \R in the section entitled "Newline - sequences" below. A change of \R setting can be combined with a change + sequences" below. A change of \R setting can be combined with a change of newline convention. Specifying what \R matches It is possible to restrict \R to match only CR, LF, or CRLF (instead of - the complete set of Unicode line endings) by setting the option - PCRE2_BSR_ANYCRLF at compile time. This effect can also be achieved by - starting a pattern with (*BSR_ANYCRLF). For completeness, (*BSR_UNI- + the complete set of Unicode line endings) by setting the option + PCRE2_BSR_ANYCRLF at compile time. This effect can also be achieved by + starting a pattern with (*BSR_ANYCRLF). For completeness, (*BSR_UNI- CODE) is also recognized, corresponding to PCRE2_BSR_UNICODE. EBCDIC CHARACTER CODES - PCRE2 can be compiled to run in an environment that uses EBCDIC as its - character code instead of ASCII or Unicode (typically a mainframe sys- - tem). In the sections below, character code values are ASCII or Uni- + PCRE2 can be compiled to run in an environment that uses EBCDIC as its + character code instead of ASCII or Unicode (typically a mainframe sys- + tem). In the sections below, character code values are ASCII or Uni- code; in an EBCDIC environment these characters may have different code values, and there are no code points greater than 255. CHARACTERS AND METACHARACTERS - A regular expression is a pattern that is matched against a subject - string from left to right. Most characters stand for themselves in a - pattern, and match the corresponding characters in the subject. As a + A regular expression is a pattern that is matched against a subject + string from left to right. Most characters stand for themselves in a + pattern, and match the corresponding characters in the subject. As a trivial example, the pattern The quick brown fox @@ -6270,11 +6090,10 @@ CHARACTERS AND METACHARACTERS caseless matching is specified (the PCRE2_CASELESS option), letters are matched independently of case. - The power of regular expressions comes from the ability to include wild - cards, character classes, alternatives, and repetitions in the pattern. - These are encoded in the pattern by the use of metacharacters, which do - not stand for themselves but instead are interpreted in some special - way. + The power of regular expressions comes from the ability to include + alternatives and repetitions in the pattern. These are encoded in the + pattern by the use of metacharacters, which do not stand for themselves + but instead are interpreted in some special way. There are two different sets of metacharacters: those that are recog- nized anywhere in the pattern except within square brackets, and those @@ -6287,11 +6106,14 @@ CHARACTERS AND METACHARACTERS . match any character except newline (by default) [ start character class definition | start of alternative branch - ( start group or control verb - ) end group or control verb + ( start subpattern + ) end subpattern + ? extends the meaning of ( + also 0 or 1 quantifier + also quantifier minimizer * 0 or more quantifier - + 1 or more quantifier; also "possessive quantifier" - ? 0 or 1 quantifier; also quantifier minimizer + + 1 or more quantifier + also "possessive quantifier" { start min/max quantifier Part of a pattern that is in square brackets is called a "character @@ -6300,7 +6122,8 @@ CHARACTERS AND METACHARACTERS \ general escape character ^ negate the class, but only if the first character - indicates character range - [ POSIX character class (if followed by POSIX syntax) + [ POSIX character class (only if followed by POSIX + syntax) ] terminates the character class The following sections describe the use of each of the metacharacters. @@ -6309,7 +6132,7 @@ CHARACTERS AND METACHARACTERS BACKSLASH The backslash character has several uses. Firstly, if it is followed by - a character that is not a digit or a letter, it takes away any special + a character that is not a number or a letter, it takes away any special meaning that character may have. This use of backslash as an escape character applies both inside and outside character classes. @@ -6320,7 +6143,7 @@ BACKSLASH that it stands for itself. In particular, if you want to match a back- slash, you write \\. - In a UTF mode, only ASCII digits and letters have any special meaning + In a UTF mode, only ASCII numbers and letters have any special meaning after a backslash. All other characters (in particular, those whose code points are greater than 127) are treated as literals. @@ -6330,14 +6153,14 @@ BACKSLASH are ignored. An escaping backslash can be used to include a white space or # character as part of the pattern. - If you want to treat all characters in a sequence as literals, you can - do so by putting them between \Q and \E. This is different from Perl in - that $ and @ are handled as literals in \Q...\E sequences in PCRE2, - whereas in Perl, $ and @ cause variable interpolation. Also, Perl does - "double-quotish backslash interpolation" on any backslashes between \Q - and \E which, its documentation says, "may lead to confusing results". - PCRE2 treats a backslash between \Q and \E just like any other charac- - ter. Note the following examples: + If you want to remove the special meaning from a sequence of charac- + ters, you can do so by putting them between \Q and \E. This is differ- + ent from Perl in that $ and @ are handled as literals in \Q...\E + sequences in PCRE2, whereas in Perl, $ and @ cause variable interpola- + tion. Also, Perl does "double-quotish backslash interpolation" on any + backslashes between \Q and \E which, its documentation says, "may lead + to confusing results". PCRE2 treats a backslash between \Q and \E just + like any other character. Note the following examples: Pattern PCRE2 matches Perl matches @@ -6362,16 +6185,15 @@ BACKSLASH acters in patterns in a visible manner. There is no restriction on the appearance of non-printing characters in a pattern, but when a pattern is being prepared by text editing, it is often easier to use one of the - following escape sequences instead of the binary character it repre- - sents. In an ASCII or Unicode environment, these escapes are as fol- - lows: + following escape sequences than the binary character it represents. In + an ASCII or Unicode environment, these escapes are as follows: \a alarm, that is, the BEL character (hex 07) \cx "control-x", where x is any printable ASCII character \e escape (hex 1B) \f form feed (hex 0C) \n linefeed (hex 0A) - \r carriage return (hex 0D) (but see below) + \r carriage return (hex 0D) \t tab (hex 09) \0dd character with octal code 0dd \ddd character with octal code ddd, or backreference @@ -6379,45 +6201,15 @@ BACKSLASH \xhh character with hex code hh \x{hhh..} character with hex code hhh.. \N{U+hhh..} character with Unicode hex code point hhh.. + \uhhhh character with hex code hhhh (when PCRE2_ALT_BSUX is set) - By default, after \x that is not followed by {, from zero to two hexa- - decimal digits are read (letters can be in upper or lower case). Any - number of hexadecimal digits may appear between \x{ and }. If a charac- - ter other than a hexadecimal digit appears between \x{ and }, or if - there is no terminating }, an error occurs. - - Characters whose code points are less than 256 can be defined by either - of the two syntaxes for \x or by an octal sequence. There is no differ- - ence in the way they are handled. For example, \xdc is exactly the same - as \x{dc} or \334. However, using the braced versions does make such - sequences easier to read. - - Support is available for some ECMAScript (aka JavaScript) escape - sequences via two compile-time options. If PCRE2_ALT_BSUX is set, the - sequence \x followed by { is not recognized. Only if \x is followed by - two hexadecimal digits is it recognized as a character escape. Other- - wise it is interpreted as a literal "x" character. In this mode, sup- - port for code points greater than 256 is provided by \u, which must be - followed by four hexadecimal digits; otherwise it is interpreted as a - literal "u" character. - - PCRE2_EXTRA_ALT_BSUX has the same effect as PCRE2_ALT_BSUX and, in - addition, \u{hhh..} is recognized as the character specified by hexa- - decimal code point. There may be any number of hexadecimal digits. - This syntax is from ECMAScript 6. - - The \N{U+hhh..} escape sequence is recognized only when the PCRE2_UTF + The \N{U+hhh..} escape sequence is recognized only when the PCRE2_UTF option is set, that is, when PCRE2 is operating in a Unicode mode. Perl - also uses \N{name} to specify characters by Unicode name; PCRE2 does - not support this. Note that when \N is not followed by an opening - brace (curly bracket) it has an entirely different meaning, matching + also uses \N{name} to specify characters by Unicode name; PCRE2 does + not support this. Note that when \N is not followed by an opening + brace (curly bracket) it has an entirely different meaning, matching any character that is not a newline. - There are some legacy applications where the escape sequence \r is - expected to match a newline. If the PCRE2_EXTRA_ESCAPED_CR_IS_LF option - is set, \r in a pattern is converted to \n so that it matches a LF - (linefeed) instead of a CR (carriage return) character. - The precise effect of \cx on ASCII characters is as follows: if x is a lower case letter, it is converted to upper case. Then bit 6 of the character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A @@ -6470,11 +6262,11 @@ BACKSLASH Outside a character class, PCRE2 reads the digit and any following dig- its as a decimal number. If the number is less than 10, begins with the - digit 8 or 9, or if there are at least that many previous capture - groups in the expression, the entire sequence is taken as a backrefer- - ence. A description of how this works is given later, following the - discussion of parenthesized groups. Otherwise, up to three octal dig- - its are read to form a character code. + digit 8 or 9, or if there are at least that many previous capturing + left parentheses in the expression, the entire sequence is taken as a + backreference. A description of how this works is given later, follow- + ing the discussion of parenthesized subpatterns. Otherwise, up to + three octal digits are read to form a character code. Inside a character class, PCRE2 handles \8 and \9 as the literal char- acters "8" and "9", and otherwise reads up to three octal digits fol- @@ -6484,7 +6276,7 @@ BACKSLASH \040 is another way of writing an ASCII space \40 is the same, provided there are fewer than 40 - previous capture groups + previous capturing subpatterns \7 is always a backreference \11 might be a backreference, or another way of writing a tab @@ -6500,6 +6292,24 @@ BACKSLASH syntax must not be introduced by a leading zero, because no more than three octal digits are ever read. + By default, after \x that is not followed by {, from zero to two hexa- + decimal digits are read (letters can be in upper or lower case). Any + number of hexadecimal digits may appear between \x{ and }. If a charac- + ter other than a hexadecimal digit appears between \x{ and }, or if + there is no terminating }, an error occurs. + + If the PCRE2_ALT_BSUX option is set, the interpretation of \x is as + just described only when it is followed by two hexadecimal digits. Oth- + erwise, it matches a literal "x" character. In this mode, support for + code points greater than 256 is provided by \u, which must be followed + by four hexadecimal digits; otherwise it matches a literal "u" charac- + ter. + + Characters whose value is less than 256 can be defined by either of the + two syntaxes for \x (or by \u in PCRE2_ALT_BSUX mode). There is no dif- + ference in the way they are handled. For example, \xdc is exactly the + same as \x{dc} (or \u00dc in PCRE2_ALT_BSUX mode). + Constraints on character values Characters that are specified using octal or hexadecimal numbers are @@ -6532,24 +6342,23 @@ BACKSLASH In Perl, the sequences \F, \l, \L, \u, and \U are recognized by its string handler and used to modify the case of following characters. By - default, PCRE2 does not support these escape sequences in patterns. - However, if either of the PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX - options is set, \U matches a "U" character, and \u can be used to - define a character by code point, as described above. + default, PCRE2 does not support these escape sequences. However, if the + PCRE2_ALT_BSUX option is set, \U matches a "U" character, and \u can be + used to define a character by code point, as described above. Absolute and relative backreferences - The sequence \g followed by a signed or unsigned number, optionally - enclosed in braces, is an absolute or relative backreference. A named - backreference can be coded as \g{name}. Backreferences are discussed - later, following the discussion of parenthesized groups. + The sequence \g followed by a signed or unsigned number, optionally + enclosed in braces, is an absolute or relative backreference. A named + backreference can be coded as \g{name}. Backreferences are discussed + later, following the discussion of parenthesized subpatterns. Absolute and relative subroutine calls - For compatibility with Oniguruma, the non-Perl syntax \g followed by a + For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or a number enclosed either in angle brackets or single quotes, is - an alternative syntax for referencing a capture group as a subroutine. - Details are discussed later. Note that \g{...} (Perl syntax) and + an alternative syntax for referencing a subpattern as a "subroutine". + Details are discussed later. Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not synonymous. The former is a backref- erence; the latter is a subroutine call. @@ -6569,58 +6378,58 @@ BACKSLASH \w any "word" character \W any "non-word" character - The \N escape sequence has the same meaning as the "." metacharacter - when PCRE2_DOTALL is not set, but setting PCRE2_DOTALL does not change + The \N escape sequence has the same meaning as the "." metacharacter + when PCRE2_DOTALL is not set, but setting PCRE2_DOTALL does not change the meaning of \N. Note that when \N is followed by an opening brace it has a different meaning. See the section entitled "Non-printing charac- - ters" above for details. Perl also uses \N{name} to specify characters + ters" above for details. Perl also uses \N{name} to specify characters by Unicode name; PCRE2 does not support this. - Each pair of lower and upper case escape sequences partitions the com- - plete set of characters into two disjoint sets. Any given character - matches one, and only one, of each pair. The sequences can appear both - inside and outside character classes. They each match one character of - the appropriate type. If the current matching point is at the end of - the subject string, all of them fail, because there is no character to + Each pair of lower and upper case escape sequences partitions the com- + plete set of characters into two disjoint sets. Any given character + matches one, and only one, of each pair. The sequences can appear both + inside and outside character classes. They each match one character of + the appropriate type. If the current matching point is at the end of + the subject string, all of them fail, because there is no character to match. - The default \s characters are HT (9), LF (10), VT (11), FF (12), CR - (13), and space (32), which are defined as white space in the "C" + The default \s characters are HT (9), LF (10), VT (11), FF (12), CR + (13), and space (32), which are defined as white space in the "C" locale. This list may vary if locale-specific matching is taking place. - For example, in some locales the "non-breaking space" character (\xA0) + For example, in some locales the "non-breaking space" character (\xA0) is recognized as white space, and in others the VT character is not. - A "word" character is an underscore or any character that is a letter - or digit. By default, the definition of letters and digits is con- + A "word" character is an underscore or any character that is a letter + or digit. By default, the definition of letters and digits is con- trolled by PCRE2's low-valued character tables, and may vary if locale- specific matching is taking place (see "Locale support" in the pcre2api - page). For example, in a French locale such as "fr_FR" in Unix-like - systems, or "french" in Windows, some character codes greater than 127 - are used for accented letters, and these are then matched by \w. The + page). For example, in a French locale such as "fr_FR" in Unix-like + systems, or "french" in Windows, some character codes greater than 127 + are used for accented letters, and these are then matched by \w. The use of locales with Unicode is discouraged. - By default, characters whose code points are greater than 127 never + By default, characters whose code points are greater than 127 never match \d, \s, or \w, and always match \D, \S, and \W, although this may - be different for characters in the range 128-255 when locale-specific - matching is happening. These escape sequences retain their original - meanings from before Unicode support was available, mainly for effi- - ciency reasons. If the PCRE2_UCP option is set, the behaviour is - changed so that Unicode properties are used to determine character + be different for characters in the range 128-255 when locale-specific + matching is happening. These escape sequences retain their original + meanings from before Unicode support was available, mainly for effi- + ciency reasons. If the PCRE2_UCP option is set, the behaviour is + changed so that Unicode properties are used to determine character types, as follows: \d any character that matches \p{Nd} (decimal digit) \s any character that matches \p{Z} or \h or \v \w any character that matches \p{L} or \p{N}, plus underscore - The upper case escapes match the inverse sets of characters. Note that - \d matches only decimal digits, whereas \w matches any Unicode digit, + The upper case escapes match the inverse sets of characters. Note that + \d matches only decimal digits, whereas \w matches any Unicode digit, as well as any Unicode letter, and underscore. Note also that PCRE2_UCP - affects \b, and \B because they are defined in terms of \w and \W. + affects \b, and \B because they are defined in terms of \w and \W. Matching these sequences is noticeably slower when PCRE2_UCP is set. - The sequences \h, \H, \v, and \V, in contrast to the other sequences, - which match only ASCII characters by default, always match a specific - list of code points, whether or not PCRE2_UCP is set. The horizontal + The sequences \h, \H, \v, and \V, in contrast to the other sequences, + which match only ASCII characters by default, always match a specific + list of code points, whether or not PCRE2_UCP is set. The horizontal space characters are: U+0009 Horizontal tab (HT) @@ -6653,36 +6462,36 @@ BACKSLASH U+2028 Line separator U+2029 Paragraph separator - In 8-bit, non-UTF-8 mode, only the characters with code points less + In 8-bit, non-UTF-8 mode, only the characters with code points less than 256 are relevant. Newline sequences - Outside a character class, by default, the escape sequence \R matches - any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent + Outside a character class, by default, the escape sequence \R matches + any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent to the following: (?>\r\n|\n|\x0b|\f|\r|\x85) - This is an example of an "atomic group", details of which are given + This is an example of an "atomic group", details of which are given below. This particular group matches either the two-character sequence - CR followed by LF, or one of the single characters LF (linefeed, - U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car- - riage return, U+000D), or NEL (next line, U+0085). Because this is an - atomic group, the two-character sequence is treated as a single unit + CR followed by LF, or one of the single characters LF (linefeed, + U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car- + riage return, U+000D), or NEL (next line, U+0085). Because this is an + atomic group, the two-character sequence is treated as a single unit that cannot be split. In other modes, two additional characters whose code points are greater than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa- - rator, U+2029). Unicode support is not needed for these characters to + rator, U+2029). Unicode support is not needed for these characters to be recognized. It is possible to restrict \R to match only CR, LF, or CRLF (instead of - the complete set of Unicode line endings) by setting the option - PCRE2_BSR_ANYCRLF at compile time. (BSR is an abbrevation for "back- + the complete set of Unicode line endings) by setting the option + PCRE2_BSR_ANYCRLF at compile time. (BSR is an abbrevation for "back- slash R".) This can be made the default when PCRE2 is built; if this is - the case, the other behaviour can be requested via the PCRE2_BSR_UNI- - CODE option. It is also possible to specify these settings by starting + the case, the other behaviour can be requested via the PCRE2_BSR_UNI- + CODE option. It is also possible to specify these settings by starting a pattern string with one of the following sequences: (*BSR_ANYCRLF) CR, LF, or CRLF only @@ -6690,77 +6499,72 @@ BACKSLASH These override the default and the options given to the compiling func- tion. Note that these special settings, which are not Perl-compatible, - are recognized only at the very start of a pattern, and that they must - be in upper case. If more than one of them is present, the last one is - used. They can be combined with a change of newline convention; for + are recognized only at the very start of a pattern, and that they must + be in upper case. If more than one of them is present, the last one is + used. They can be combined with a change of newline convention; for example, a pattern can start with: (*ANY)(*BSR_ANYCRLF) - They can also be combined with the (*UTF) or (*UCP) special sequences. - Inside a character class, \R is treated as an unrecognized escape + They can also be combined with the (*UTF) or (*UCP) special sequences. + Inside a character class, \R is treated as an unrecognized escape sequence, and causes an error. Unicode character properties - When PCRE2 is built with Unicode support (the default), three addi- - tional escape sequences that match characters with specific properties - are available. They can be used in any mode, though in 8-bit and 16-bit - non-UTF modes these sequences are of course limited to testing charac- - ters whose code points are less than U+0100 and U+10000, respectively. - In 32-bit non-UTF mode, code points greater than 0x10ffff (the Unicode - limit) may be encountered. These are all treated as being in the - Unknown script and with an unassigned type. The extra escape sequences - are: + When PCRE2 is built with Unicode support (the default), three addi- + tional escape sequences that match characters with specific properties + are available. In 8-bit non-UTF-8 mode, these sequences are of course + limited to testing characters whose code points are less than 256, but + they do work in this mode. In 32-bit non-UTF mode, code points greater + than 0x10ffff (the Unicode limit) may be encountered. These are all + treated as being in the Common script and with an unassigned type. The + extra escape sequences are: \p{xx} a character with the xx property \P{xx} a character without the xx property \X a Unicode extended grapheme cluster - The property names represented by xx above are case-sensitive. There is - support for Unicode script names, Unicode general category properties, - "Any", which matches any character (including newline), and some spe- - cial PCRE2 properties (described in the next section). Other Perl - properties such as "InMusicalSymbols" are not supported by PCRE2. Note - that \P{Any} does not match any characters, so always causes a match - failure. + The property names represented by xx above are limited to the Unicode + script names, the general category properties, "Any", which matches any + character (including newline), and some special PCRE2 properties + (described in the next section). Other Perl properties such as "InMu- + sicalSymbols" are not supported by PCRE2. Note that \P{Any} does not + match any characters, so always causes a match failure. Sets of Unicode characters are defined as belonging to certain scripts. - A character from one of these sets can be matched using a script name. + A character from one of these sets can be matched using a script name. For example: \p{Greek} \P{Han} - Unassigned characters (and in non-UTF 32-bit mode, characters with code - points greater than 0x10FFFF) are assigned the "Unknown" script. Others - that are not part of an identified script are lumped together as "Com- - mon". The current list of scripts is: - - Adlam, Ahom, Anatolian_Hieroglyphs, Arabic, Armenian, Avestan, Bali- - nese, Bamum, Bassa_Vah, Batak, Bengali, Bhaiksuki, Bopomofo, Brahmi, - Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Caucasian_Alba- - nian, Chakma, Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, - Cyrillic, Deseret, Devanagari, Dogra, Duployan, Egyptian_Hieroglyphs, - Elbasan, Ethiopic, Georgian, Glagolitic, Gothic, Grantha, Greek, - Gujarati, Gunjala_Gondi, Gurmukhi, Han, Hangul, Hanifi_Rohingya, - Hanunoo, Hatran, Hebrew, Hiragana, Imperial_Aramaic, Inherited, - Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi, Kan- - nada, Katakana, Kayah_Li, Kharoshthi, Khmer, Khojki, Khudawadi, Lao, - Latin, Lepcha, Limbu, Linear_A, Linear_B, Lisu, Lycian, Lydian, Maha- - jani, Makasar, Malayalam, Mandaic, Manichaean, Marchen, Masaram_Gondi, + Those that are not part of an identified script are lumped together as + "Common". The current list of scripts is: + + Adlam, Ahom, Anatolian_Hieroglyphs, Arabic, Armenian, Avestan, Bali- + nese, Bamum, Bassa_Vah, Batak, Bengali, Bhaiksuki, Bopomofo, Brahmi, + Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Caucasian_Alba- + nian, Chakma, Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, + Cyrillic, Deseret, Devanagari, Dogra, Duployan, Egyptian_Hieroglyphs, + Elbasan, Ethiopic, Georgian, Glagolitic, Gothic, Grantha, Greek, + Gujarati, Gunjala_Gondi, Gurmukhi, Han, Hangul, Hanifi_Rohingya, + Hanunoo, Hatran, Hebrew, Hiragana, Imperial_Aramaic, Inherited, + Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi, Kan- + nada, Katakana, Kayah_Li, Kharoshthi, Khmer, Khojki, Khudawadi, Lao, + Latin, Lepcha, Limbu, Linear_A, Linear_B, Lisu, Lycian, Lydian, Maha- + jani, Makasar, Malayalam, Mandaic, Manichaean, Marchen, Masaram_Gondi, Medefaidrin, Meetei_Mayek, Mende_Kikakui, Meroitic_Cursive, - Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro, Multani, Myanmar, - Nabataean, New_Tai_Lue, Newa, Nko, Nushu, Ogham, Ol_Chiki, Old_Hungar- - ian, Old_Italic, Old_North_Arabian, Old_Permic, Old_Persian, Old_Sog- - dian, Old_South_Arabian, Old_Turkic, Oriya, Osage, Osmanya, + Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro, Multani, Myanmar, + Nabataean, New_Tai_Lue, Newa, Nko, Nushu, Ogham, Ol_Chiki, Old_Hungar- + ian, Old_Italic, Old_North_Arabian, Old_Permic, Old_Persian, Old_Sog- + dian, Old_South_Arabian, Old_Turkic, Oriya, Osage, Osmanya, Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa, Phoenician, - Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra, Sharada, Sha- - vian, Siddham, SignWriting, Sinhala, Sogdian, Sora_Sompeng, Soyombo, - Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, - Tai_Viet, Takri, Tamil, Tangut, Telugu, Thaana, Thai, Tibetan, Tifi- - nagh, Tirhuta, Ugaritic, Unknown, Vai, Warang_Citi, Yi, Zan- - abazar_Square. + Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra, Sharada, Sha- + vian, Siddham, SignWriting, Sinhala, Sogdian, Sora_Sompeng, Soyombo, + Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, + Tai_Viet, Takri, Tamil, Tangut, Telugu, Thaana, Thai, Tibetan, Tifi- + nagh, Tirhuta, Ugaritic, Vai, Warang_Citi, Yi, Zanabazar_Square. Each character has exactly one Unicode general category property, spec- ified by a two-letter abbreviation. For compatibility with Perl, nega- @@ -6826,13 +6630,11 @@ BACKSLASH has the Lu, Ll, or Lt property, in other words, a letter that is not classified as a modifier or "other". - The Cs (Surrogate) property applies only to characters whose code - points are in the range U+D800 to U+DFFF. These characters are no dif- - ferent to any other character when PCRE2 is not in UTF mode (using the - 16-bit or 32-bit library). However, they are not valid in Unicode - strings and so cannot be tested by PCRE2 in UTF mode, unless UTF valid- - ity checking has been turned off (see the discussion of - PCRE2_NO_UTF_CHECK in the pcre2api page). + The Cs (Surrogate) property applies only to characters in the range + U+D800 to U+DFFF. Such characters are not valid in Unicode strings and + so cannot be tested by PCRE2, unless UTF validity checking has been + turned off (see the discussion of PCRE2_NO_UTF_CHECK in the pcre2api + page). Perl does not support the Cs property. The long synonyms for property names that Perl supports (such as \p{Letter}) are not supported by PCRE2, nor is it permitted to prefix @@ -6973,8 +6775,8 @@ BACKSLASH The final use of backslash is for certain simple assertions. An asser- tion specifies a condition that has to be met at a particular point in a match, without consuming any characters from the subject string. The - use of groups for more complicated assertions is described below. The - backslashed assertions are: + use of subpatterns for more complicated assertions is described below. + The backslashed assertions are: \b matches at a word boundary \B matches when not at a word boundary @@ -6991,184 +6793,183 @@ BACKSLASH A word boundary is a position in the subject string where the current character and the previous character do not both match \w or \W (i.e. one matches \w and the other matches \W), or the start or end of the - string if the first or last character matches \w, respectively. When - PCRE2 is built with Unicode support, the meanings of \w and \W can be - changed by setting the PCRE2_UCP option. When this is done, it also - affects \b and \B. Neither PCRE2 nor Perl has a separate "start of - word" or "end of word" metasequence. However, whatever follows \b nor- - mally determines which it is. For example, the fragment \ba matches "a" - at the start of a word. - - The \A, \Z, and \z assertions differ from the traditional circumflex + string if the first or last character matches \w, respectively. In a + UTF mode, the meanings of \w and \W can be changed by setting the + PCRE2_UCP option. When this is done, it also affects \b and \B. Neither + PCRE2 nor Perl has a separate "start of word" or "end of word" metase- + quence. However, whatever follows \b normally determines which it is. + For example, the fragment \ba matches "a" at the start of a word. + + The \A, \Z, and \z assertions differ from the traditional circumflex and dollar (described in the next section) in that they only ever match - at the very start and end of the subject string, whatever options are - set. Thus, they are independent of multiline mode. These three asser- - tions are not affected by the PCRE2_NOTBOL or PCRE2_NOTEOL options, - which affect only the behaviour of the circumflex and dollar metachar- - acters. However, if the startoffset argument of pcre2_match() is non- - zero, indicating that matching is to start at a point other than the - beginning of the subject, \A can never match. The difference between - \Z and \z is that \Z matches before a newline at the end of the string + at the very start and end of the subject string, whatever options are + set. Thus, they are independent of multiline mode. These three asser- + tions are not affected by the PCRE2_NOTBOL or PCRE2_NOTEOL options, + which affect only the behaviour of the circumflex and dollar metachar- + acters. However, if the startoffset argument of pcre2_match() is non- + zero, indicating that matching is to start at a point other than the + beginning of the subject, \A can never match. The difference between + \Z and \z is that \Z matches before a newline at the end of the string as well as at the very end, whereas \z matches only at the end. - The \G assertion is true only when the current matching position is at - the start point of the matching process, as specified by the startoff- - set argument of pcre2_match(). It differs from \A when the value of - startoffset is non-zero. By calling pcre2_match() multiple times with - appropriate arguments, you can mimic Perl's /g option, and it is in + The \G assertion is true only when the current matching position is at + the start point of the matching process, as specified by the startoff- + set argument of pcre2_match(). It differs from \A when the value of + startoffset is non-zero. By calling pcre2_match() multiple times with + appropriate arguments, you can mimic Perl's /g option, and it is in this kind of implementation where \G can be useful. - Note, however, that PCRE2's implementation of \G, being true at the - starting character of the matching process, is subtly different from - Perl's, which defines it as true at the end of the previous match. In - Perl, these can be different when the previously matched string was + Note, however, that PCRE2's implementation of \G, being true at the + starting character of the matching process, is subtly different from + Perl's, which defines it as true at the end of the previous match. In + Perl, these can be different when the previously matched string was empty. Because PCRE2 does just one match at a time, it cannot reproduce this behaviour. - If all the alternatives of a pattern begin with \G, the expression is + If all the alternatives of a pattern begin with \G, the expression is anchored to the starting match position, and the "anchored" flag is set in the compiled regular expression. CIRCUMFLEX AND DOLLAR - The circumflex and dollar metacharacters are zero-width assertions. - That is, they test for a particular condition being true without con- + The circumflex and dollar metacharacters are zero-width assertions. + That is, they test for a particular condition being true without con- suming any characters from the subject string. These two metacharacters - are concerned with matching the starts and ends of lines. If the new- - line convention is set so that only the two-character sequence CRLF is - recognized as a newline, isolated CR and LF characters are treated as + are concerned with matching the starts and ends of lines. If the new- + line convention is set so that only the two-character sequence CRLF is + recognized as a newline, isolated CR and LF characters are treated as ordinary data characters, and are not recognized as newlines. Outside a character class, in the default matching mode, the circumflex - character is an assertion that is true only if the current matching - point is at the start of the subject string. If the startoffset argu- - ment of pcre2_match() is non-zero, or if PCRE2_NOTBOL is set, circum- - flex can never match if the PCRE2_MULTILINE option is unset. Inside a - character class, circumflex has an entirely different meaning (see + character is an assertion that is true only if the current matching + point is at the start of the subject string. If the startoffset argu- + ment of pcre2_match() is non-zero, or if PCRE2_NOTBOL is set, circum- + flex can never match if the PCRE2_MULTILINE option is unset. Inside a + character class, circumflex has an entirely different meaning (see below). - Circumflex need not be the first character of the pattern if a number - of alternatives are involved, but it should be the first thing in each - alternative in which it appears if the pattern is ever to match that - branch. If all possible alternatives start with a circumflex, that is, - if the pattern is constrained to match only at the start of the sub- - ject, it is said to be an "anchored" pattern. (There are also other + Circumflex need not be the first character of the pattern if a number + of alternatives are involved, but it should be the first thing in each + alternative in which it appears if the pattern is ever to match that + branch. If all possible alternatives start with a circumflex, that is, + if the pattern is constrained to match only at the start of the sub- + ject, it is said to be an "anchored" pattern. (There are also other constructs that can cause a pattern to be anchored.) - The dollar character is an assertion that is true only if the current - matching point is at the end of the subject string, or immediately - before a newline at the end of the string (by default), unless + The dollar character is an assertion that is true only if the current + matching point is at the end of the subject string, or immediately + before a newline at the end of the string (by default), unless PCRE2_NOTEOL is set. Note, however, that it does not actually match the newline. Dollar need not be the last character of the pattern if a num- ber of alternatives are involved, but it should be the last item in any - branch in which it appears. Dollar has no special meaning in a charac- + branch in which it appears. Dollar has no special meaning in a charac- ter class. - The meaning of dollar can be changed so that it matches only at the - very end of the string, by setting the PCRE2_DOLLAR_ENDONLY option at + The meaning of dollar can be changed so that it matches only at the + very end of the string, by setting the PCRE2_DOLLAR_ENDONLY option at compile time. This does not affect the \Z assertion. The meanings of the circumflex and dollar metacharacters are changed if - the PCRE2_MULTILINE option is set. When this is the case, a dollar - character matches before any newlines in the string, as well as at the - very end, and a circumflex matches immediately after internal newlines - as well as at the start of the subject string. It does not match after - a newline that ends the string, for compatibility with Perl. However, + the PCRE2_MULTILINE option is set. When this is the case, a dollar + character matches before any newlines in the string, as well as at the + very end, and a circumflex matches immediately after internal newlines + as well as at the start of the subject string. It does not match after + a newline that ends the string, for compatibility with Perl. However, this can be changed by setting the PCRE2_ALT_CIRCUMFLEX option. - For example, the pattern /^abc$/ matches the subject string "def\nabc" - (where \n represents a newline) in multiline mode, but not otherwise. - Consequently, patterns that are anchored in single line mode because - all branches start with ^ are not anchored in multiline mode, and a - match for circumflex is possible when the startoffset argument of - pcre2_match() is non-zero. The PCRE2_DOLLAR_ENDONLY option is ignored + For example, the pattern /^abc$/ matches the subject string "def\nabc" + (where \n represents a newline) in multiline mode, but not otherwise. + Consequently, patterns that are anchored in single line mode because + all branches start with ^ are not anchored in multiline mode, and a + match for circumflex is possible when the startoffset argument of + pcre2_match() is non-zero. The PCRE2_DOLLAR_ENDONLY option is ignored if PCRE2_MULTILINE is set. - When the newline convention (see "Newline conventions" below) recog- - nizes the two-character sequence CRLF as a newline, this is preferred, - even if the single characters CR and LF are also recognized as new- - lines. For example, if the newline convention is "any", a multiline - mode circumflex matches before "xyz" in the string "abc\r\nxyz" rather - than after CR, even though CR on its own is a valid newline. (It also + When the newline convention (see "Newline conventions" below) recog- + nizes the two-character sequence CRLF as a newline, this is preferred, + even if the single characters CR and LF are also recognized as new- + lines. For example, if the newline convention is "any", a multiline + mode circumflex matches before "xyz" in the string "abc\r\nxyz" rather + than after CR, even though CR on its own is a valid newline. (It also matches at the very start of the string, of course.) - Note that the sequences \A, \Z, and \z can be used to match the start - and end of the subject in both modes, and if all branches of a pattern - start with \A it is always anchored, whether or not PCRE2_MULTILINE is + Note that the sequences \A, \Z, and \z can be used to match the start + and end of the subject in both modes, and if all branches of a pattern + start with \A it is always anchored, whether or not PCRE2_MULTILINE is set. FULL STOP (PERIOD, DOT) AND \N Outside a character class, a dot in the pattern matches any one charac- - ter in the subject string except (by default) a character that signi- + ter in the subject string except (by default) a character that signi- fies the end of a line. - When a line ending is defined as a single character, dot never matches - that character; when the two-character sequence CRLF is used, dot does - not match CR if it is immediately followed by LF, but otherwise it - matches all characters (including isolated CRs and LFs). When any Uni- - code line endings are being recognized, dot does not match CR or LF or + When a line ending is defined as a single character, dot never matches + that character; when the two-character sequence CRLF is used, dot does + not match CR if it is immediately followed by LF, but otherwise it + matches all characters (including isolated CRs and LFs). When any Uni- + code line endings are being recognized, dot does not match CR or LF or any of the other line ending characters. - The behaviour of dot with regard to newlines can be changed. If the - PCRE2_DOTALL option is set, a dot matches any one character, without - exception. If the two-character sequence CRLF is present in the sub- + The behaviour of dot with regard to newlines can be changed. If the + PCRE2_DOTALL option is set, a dot matches any one character, without + exception. If the two-character sequence CRLF is present in the sub- ject string, it takes two dots to match it. - The handling of dot is entirely independent of the handling of circum- - flex and dollar, the only relationship being that they both involve + The handling of dot is entirely independent of the handling of circum- + flex and dollar, the only relationship being that they both involve newlines. Dot has no special meaning in a character class. - The escape sequence \N when not followed by an opening brace behaves - like a dot, except that it is not affected by the PCRE2_DOTALL option. - In other words, it matches any character except one that signifies the + The escape sequence \N when not followed by an opening brace behaves + like a dot, except that it is not affected by the PCRE2_DOTALL option. + In other words, it matches any character except one that signifies the end of a line. When \N is followed by an opening brace it has a different meaning. See - the section entitled "Non-printing characters" above for details. Perl - also uses \N{name} to specify characters by Unicode name; PCRE2 does + the section entitled "Non-printing characters" above for details. Perl + also uses \N{name} to specify characters by Unicode name; PCRE2 does not support this. MATCHING A SINGLE CODE UNIT - Outside a character class, the escape sequence \C matches any one code - unit, whether or not a UTF mode is set. In the 8-bit library, one code - unit is one byte; in the 16-bit library it is a 16-bit unit; in the - 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches - line-ending characters. The feature is provided in Perl in order to + Outside a character class, the escape sequence \C matches any one code + unit, whether or not a UTF mode is set. In the 8-bit library, one code + unit is one byte; in the 16-bit library it is a 16-bit unit; in the + 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches + line-ending characters. The feature is provided in Perl in order to match individual bytes in UTF-8 mode, but it is unclear how it can use- fully be used. - Because \C breaks up characters into individual code units, matching - one unit with \C in UTF-8 or UTF-16 mode means that the rest of the - string may start with a malformed UTF character. This has undefined + Because \C breaks up characters into individual code units, matching + one unit with \C in UTF-8 or UTF-16 mode means that the rest of the + string may start with a malformed UTF character. This has undefined results, because PCRE2 assumes that it is matching character by charac- - ter in a valid UTF string (by default it checks the subject string's - validity at the start of processing unless the PCRE2_NO_UTF_CHECK + ter in a valid UTF string (by default it checks the subject string's + validity at the start of processing unless the PCRE2_NO_UTF_CHECK option is used). - An application can lock out the use of \C by setting the - PCRE2_NEVER_BACKSLASH_C option when compiling a pattern. It is also + An application can lock out the use of \C by setting the + PCRE2_NEVER_BACKSLASH_C option when compiling a pattern. It is also possible to build PCRE2 with the use of \C permanently disabled. - PCRE2 does not allow \C to appear in lookbehind assertions (described - below) in UTF-8 or UTF-16 modes, because this would make it impossible - to calculate the length of the lookbehind. Neither the alternative + PCRE2 does not allow \C to appear in lookbehind assertions (described + below) in UTF-8 or UTF-16 modes, because this would make it impossible + to calculate the length of the lookbehind. Neither the alternative matching function pcre2_dfa_match() nor the JIT optimizer support \C in these UTF modes. The former gives a match-time error; the latter fails to optimize and so the match is always run using the interpreter. - In the 32-bit library, however, \C is always supported (when not - explicitly locked out) because it always matches a single code unit, + In the 32-bit library, however, \C is always supported (when not + explicitly locked out) because it always matches a single code unit, whether or not UTF-32 is specified. In general, the \C escape sequence is best avoided. However, one way of - using it that avoids the problem of malformed UTF-8 or UTF-16 charac- - ters is to use a lookahead to check the length of the next character, - as in this pattern, which could be used with a UTF-8 string (ignore + using it that avoids the problem of malformed UTF-8 or UTF-16 charac- + ters is to use a lookahead to check the length of the next character, + as in this pattern, which could be used with a UTF-8 string (ignore white space and line breaks): (?| (?=[\x00-\x7f])(\C) | @@ -7176,11 +6977,11 @@ MATCHING A SINGLE CODE UNIT (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) | (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C)) - In this example, a group that starts with (?| resets the capturing - parentheses numbers in each alternative (see "Duplicate Group Numbers" - below). The assertions at the start of each branch check the next UTF-8 - character for values whose encoding uses 1, 2, 3, or 4 bytes, respec- - tively. The character's individual bytes are then captured by the + In this example, a group that starts with (?| resets the capturing + parentheses numbers in each alternative (see "Duplicate Subpattern Num- + bers" below). The assertions at the start of each branch check the next + UTF-8 character for values whose encoding uses 1, 2, 3, or 4 bytes, + respectively. The character's individual bytes are then captured by the appropriate number of \C groups. @@ -7188,115 +6989,115 @@ SQUARE BRACKETS AND CHARACTER CLASSES An opening square bracket introduces a character class, terminated by a closing square bracket. A closing square bracket on its own is not spe- - cial by default. If a closing square bracket is required as a member + cial by default. If a closing square bracket is required as a member of the class, it should be the first data character in the class (after - an initial circumflex, if present) or escaped with a backslash. This - means that, by default, an empty class cannot be defined. However, if - the PCRE2_ALLOW_EMPTY_CLASS option is set, a closing square bracket at + an initial circumflex, if present) or escaped with a backslash. This + means that, by default, an empty class cannot be defined. However, if + the PCRE2_ALLOW_EMPTY_CLASS option is set, a closing square bracket at the start does end the (empty) class. - A character class matches a single character in the subject. A matched + A character class matches a single character in the subject. A matched character must be in the set of characters defined by the class, unless - the first character in the class definition is a circumflex, in which + the first character in the class definition is a circumflex, in which case the subject character must not be in the set defined by the class. - If a circumflex is actually required as a member of the class, ensure + If a circumflex is actually required as a member of the class, ensure it is not the first character, or escape it with a backslash. - For example, the character class [aeiou] matches any lower case vowel, - while [^aeiou] matches any character that is not a lower case vowel. + For example, the character class [aeiou] matches any lower case vowel, + while [^aeiou] matches any character that is not a lower case vowel. Note that a circumflex is just a convenient notation for specifying the - characters that are in the class by enumerating those that are not. A - class that starts with a circumflex is not an assertion; it still con- - sumes a character from the subject string, and therefore it fails if + characters that are in the class by enumerating those that are not. A + class that starts with a circumflex is not an assertion; it still con- + sumes a character from the subject string, and therefore it fails if the current pointer is at the end of the string. - Characters in a class may be specified by their code points using \o, - \x, or \N{U+hh..} in the usual way. When caseless matching is set, any - letters in a class represent both their upper case and lower case ver- - sions, so for example, a caseless [aeiou] matches "A" as well as "a", - and a caseless [^aeiou] does not match "A", whereas a caseful version + Characters in a class may be specified by their code points using \o, + \x, or \N{U+hh..} in the usual way. When caseless matching is set, any + letters in a class represent both their upper case and lower case ver- + sions, so for example, a caseless [aeiou] matches "A" as well as "a", + and a caseless [^aeiou] does not match "A", whereas a caseful version would. - Characters that might indicate line breaks are never treated in any - special way when matching character classes, whatever line-ending - sequence is in use, and whatever setting of the PCRE2_DOTALL and - PCRE2_MULTILINE options is used. A class such as [^a] always matches + Characters that might indicate line breaks are never treated in any + special way when matching character classes, whatever line-ending + sequence is in use, and whatever setting of the PCRE2_DOTALL and + PCRE2_MULTILINE options is used. A class such as [^a] always matches one of these characters. The generic character type escape sequences \d, \D, \h, \H, \p, \P, \s, - \S, \v, \V, \w, and \W may appear in a character class, and add the - characters that they match to the class. For example, [\dABCDEF] - matches any hexadecimal digit. In UTF modes, the PCRE2_UCP option - affects the meanings of \d, \s, \w and their upper case partners, just - as it does when they appear outside a character class, as described in - the section entitled "Generic character types" above. The escape - sequence \b has a different meaning inside a character class; it - matches the backspace character. The sequences \B, \R, and \X are not - special inside a character class. Like any other unrecognized escape - sequences, they cause an error. The same is true for \N when not fol- + \S, \v, \V, \w, and \W may appear in a character class, and add the + characters that they match to the class. For example, [\dABCDEF] + matches any hexadecimal digit. In UTF modes, the PCRE2_UCP option + affects the meanings of \d, \s, \w and their upper case partners, just + as it does when they appear outside a character class, as described in + the section entitled "Generic character types" above. The escape + sequence \b has a different meaning inside a character class; it + matches the backspace character. The sequences \B, \R, and \X are not + special inside a character class. Like any other unrecognized escape + sequences, they cause an error. The same is true for \N when not fol- lowed by an opening brace. - The minus (hyphen) character can be used to specify a range of charac- - ters in a character class. For example, [d-m] matches any letter - between d and m, inclusive. If a minus character is required in a - class, it must be escaped with a backslash or appear in a position - where it cannot be interpreted as indicating a range, typically as the + The minus (hyphen) character can be used to specify a range of charac- + ters in a character class. For example, [d-m] matches any letter + between d and m, inclusive. If a minus character is required in a + class, it must be escaped with a backslash or appear in a position + where it cannot be interpreted as indicating a range, typically as the first or last character in the class, or immediately after a range. For - example, [b-d-z] matches letters in the range b to d, a hyphen charac- + example, [b-d-z] matches letters in the range b to d, a hyphen charac- ter, or z. Perl treats a hyphen as a literal if it appears before or after a POSIX class (see below) or before or after a character type escape such as as - \d or \H. However, unless the hyphen is the last character in the - class, Perl outputs a warning in its warning mode, as this is most - likely a user error. As PCRE2 has no facility for warning, an error is + \d or \H. However, unless the hyphen is the last character in the + class, Perl outputs a warning in its warning mode, as this is most + likely a user error. As PCRE2 has no facility for warning, an error is given in these cases. It is not possible to have the literal character "]" as the end charac- - ter of a range. A pattern such as [W-]46] is interpreted as a class of - two characters ("W" and "-") followed by a literal string "46]", so it - would match "W46]" or "-46]". However, if the "]" is escaped with a - backslash it is interpreted as the end of range, so [W-\]46] is inter- - preted as a class containing a range followed by two other characters. - The octal or hexadecimal representation of "]" can also be used to end + ter of a range. A pattern such as [W-]46] is interpreted as a class of + two characters ("W" and "-") followed by a literal string "46]", so it + would match "W46]" or "-46]". However, if the "]" is escaped with a + backslash it is interpreted as the end of range, so [W-\]46] is inter- + preted as a class containing a range followed by two other characters. + The octal or hexadecimal representation of "]" can also be used to end a range. Ranges normally include all code points between the start and end char- - acters, inclusive. They can also be used for code points specified + acters, inclusive. They can also be used for code points specified numerically, for example [\000-\037]. Ranges can include any characters - that are valid for the current mode. In any UTF mode, the so-called - "surrogate" characters (those whose code points lie between 0xd800 and - 0xdfff inclusive) may not be specified explicitly by default (the - PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES option disables this check). How- + that are valid for the current mode. In any UTF mode, the so-called + "surrogate" characters (those whose code points lie between 0xd800 and + 0xdfff inclusive) may not be specified explicitly by default (the + PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES option disables this check). How- ever, ranges such as [\x{d7ff}-\x{e000}], which include the surrogates, are always permitted. - There is a special case in EBCDIC environments for ranges whose end + There is a special case in EBCDIC environments for ranges whose end points are both specified as literal letters in the same case. For com- - patibility with Perl, EBCDIC code points within the range that are not - letters are omitted. For example, [h-k] matches only four characters, + patibility with Perl, EBCDIC code points within the range that are not + letters are omitted. For example, [h-k] matches only four characters, even though the codes for h and k are 0x88 and 0x92, a range of 11 code - points. However, if the range is specified numerically, for example, + points. However, if the range is specified numerically, for example, [\x88-\x92] or [h-\x92], all code points are included. If a range that includes letters is used when caseless matching is set, it matches the letters in either case. For example, [W-c] is equivalent - to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if - character tables for a French locale are in use, [\xc8-\xcb] matches + to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if + character tables for a French locale are in use, [\xc8-\xcb] matches accented E characters in both cases. - A circumflex can conveniently be used with the upper case character - types to specify a more restricted set of characters than the matching - lower case type. For example, the class [^\W_] matches any letter or + A circumflex can conveniently be used with the upper case character + types to specify a more restricted set of characters than the matching + lower case type. For example, the class [^\W_] matches any letter or digit, but not underscore, whereas [\w] includes underscore. A positive character class should be read as "something OR something OR ..." and a negative class as "NOT something AND NOT something AND NOT ...". - The only metacharacters that are recognized in character classes are - backslash, hyphen (only where it can be interpreted as specifying a - range), circumflex (only at the start), opening square bracket (only - when it can be interpreted as introducing a POSIX class name, or for a - special compatibility feature - see the next two sections), and the + The only metacharacters that are recognized in character classes are + backslash, hyphen (only where it can be interpreted as specifying a + range), circumflex (only at the start), opening square bracket (only + when it can be interpreted as introducing a POSIX class name, or for a + special compatibility feature - see the next two sections), and the terminating closing square bracket. However, escaping other non- alphanumeric characters does no harm. @@ -7304,7 +7105,7 @@ SQUARE BRACKETS AND CHARACTER CLASSES POSIX CHARACTER CLASSES Perl supports the POSIX notation for character classes. This uses names - enclosed by [: and :] within the enclosing square brackets. PCRE2 also + enclosed by [: and :] within the enclosing square brackets. PCRE2 also supports this notation. For example, [01[:alpha:]%] @@ -7327,13 +7128,13 @@ POSIX CHARACTER CLASSES word "word" characters (same as \w) xdigit hexadecimal digits - The default "space" characters are HT (9), LF (10), VT (11), FF (12), - CR (13), and space (32). If locale-specific matching is taking place, - the list of space characters may be different; there may be fewer or + The default "space" characters are HT (9), LF (10), VT (11), FF (12), + CR (13), and space (32). If locale-specific matching is taking place, + the list of space characters may be different; there may be fewer or more of them. "Space" and \s match the same set of characters. - The name "word" is a Perl extension, and "blank" is a GNU extension - from Perl 5.8. Another Perl extension is negation, which is indicated + The name "word" is a Perl extension, and "blank" is a GNU extension + from Perl 5.8. Another Perl extension is negation, which is indicated by a ^ character after the colon. For example, [12[:^digit:]] @@ -7344,9 +7145,9 @@ POSIX CHARACTER CLASSES By default, characters with values greater than 127 do not match any of the POSIX character classes, although this may be different for charac- - ters in the range 128-255 when locale-specific matching is happening. - However, if the PCRE2_UCP option is passed to pcre2_compile(), some of - the classes are changed so that Unicode character properties are used. + ters in the range 128-255 when locale-specific matching is happening. + However, if the PCRE2_UCP option is passed to pcre2_compile(), some of + the classes are changed so that Unicode character properties are used. This is achieved by replacing certain POSIX classes with other sequences, as follows: @@ -7360,10 +7161,10 @@ POSIX CHARACTER CLASSES [:upper:] becomes \p{Lu} [:word:] becomes \p{Xwd} - Negated versions, such as [:^alpha:] use \P instead of \p. Three other + Negated versions, such as [:^alpha:] use \P instead of \p. Three other POSIX classes are handled specially in UCP mode: - [:graph:] This matches characters that have glyphs that mark the page + [:graph:] This matches characters that have glyphs that mark the page when printed. In Unicode property terms, it matches all char- acters with the L, M, N, P, S, or Cf properties, except for: @@ -7372,60 +7173,60 @@ POSIX CHARACTER CLASSES U+2066 - U+2069 Various "isolate"s - [:print:] This matches the same characters as [:graph:] plus space - characters that are not controls, that is, characters with + [:print:] This matches the same characters as [:graph:] plus space + characters that are not controls, that is, characters with the Zs property. [:punct:] This matches all characters that have the Unicode P (punctua- - tion) property, plus those characters with code points less + tion) property, plus those characters with code points less than 256 that have the S (Symbol) property. - The other POSIX classes are unchanged, and match only characters with + The other POSIX classes are unchanged, and match only characters with code points less than 256. COMPATIBILITY FEATURE FOR WORD BOUNDARIES - In the POSIX.2 compliant library that was included in 4.4BSD Unix, the - ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word" + In the POSIX.2 compliant library that was included in 4.4BSD Unix, the + ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word" and "end of word". PCRE2 treats these items as follows: [[:<:]] is converted to \b(?=\w) [[:>:]] is converted to \b(?<=\w) Only these exact character sequences are recognized. A sequence such as - [a[:<:]b] provokes error for an unrecognized POSIX class name. This - support is not compatible with Perl. It is provided to help migrations + [a[:<:]b] provokes error for an unrecognized POSIX class name. This + support is not compatible with Perl. It is provided to help migrations from other environments, and is best not used in any new patterns. Note - that \b matches at the start and the end of a word (see "Simple asser- - tions" above), and in a Perl-style pattern the preceding or following - character normally shows which is wanted, without the need for the - assertions that are used above in order to give exactly the POSIX be- + that \b matches at the start and the end of a word (see "Simple asser- + tions" above), and in a Perl-style pattern the preceding or following + character normally shows which is wanted, without the need for the + assertions that are used above in order to give exactly the POSIX be- haviour. VERTICAL BAR - Vertical bar characters are used to separate alternative patterns. For + Vertical bar characters are used to separate alternative patterns. For example, the pattern gilbert|sullivan - matches either "gilbert" or "sullivan". Any number of alternatives may - appear, and an empty alternative is permitted (matching the empty + matches either "gilbert" or "sullivan". Any number of alternatives may + appear, and an empty alternative is permitted (matching the empty string). The matching process tries each alternative in turn, from left - to right, and the first one that succeeds is used. If the alternatives - are within a group (defined below), "succeeds" means matching the rest - of the main pattern as well as the alternative in the group. + to right, and the first one that succeeds is used. If the alternatives + are within a subpattern (defined below), "succeeds" means matching the + rest of the main pattern as well as the alternative in the subpattern. INTERNAL OPTION SETTING - The settings of the PCRE2_CASELESS, PCRE2_MULTILINE, PCRE2_DOTALL, - PCRE2_EXTENDED, PCRE2_EXTENDED_MORE, and PCRE2_NO_AUTO_CAPTURE options - can be changed from within the pattern by a sequence of letters - enclosed between "(?" and ")". These options are Perl-compatible, and - are described in detail in the pcre2api documentation. The option let- + The settings of the PCRE2_CASELESS, PCRE2_MULTILINE, PCRE2_DOTALL, + PCRE2_EXTENDED, PCRE2_EXTENDED_MORE, and PCRE2_NO_AUTO_CAPTURE options + can be changed from within the pattern by a sequence of letters + enclosed between "(?" and ")". These options are Perl-compatible, and + are described in detail in the pcre2api documentation. The option let- ters are: i for PCRE2_CASELESS @@ -7436,73 +7237,72 @@ INTERNAL OPTION SETTING xx for PCRE2_EXTENDED_MORE For example, (?im) sets caseless, multiline matching. It is also possi- - ble to unset these options by preceding the relevant letters with a + ble to unset these options by preceding the relevant letters with a hyphen, for example (?-im). The two "extended" options are not indepen- dent; unsetting either one cancels the effects of both of them. - A combined setting and unsetting such as (?im-sx), which sets - PCRE2_CASELESS and PCRE2_MULTILINE while unsetting PCRE2_DOTALL and - PCRE2_EXTENDED, is also permitted. Only one hyphen may appear in the - options string. If a letter appears both before and after the hyphen, - the option is unset. An empty options setting "(?)" is allowed. Need- + A combined setting and unsetting such as (?im-sx), which sets + PCRE2_CASELESS and PCRE2_MULTILINE while unsetting PCRE2_DOTALL and + PCRE2_EXTENDED, is also permitted. Only one hyphen may appear in the + options string. If a letter appears both before and after the hyphen, + the option is unset. An empty options setting "(?)" is allowed. Need- less to say, it has no effect. - If the first character following (? is a circumflex, it causes all of - the above options to be unset. Thus, (?^) is equivalent to (?-imnsx). - Letters may follow the circumflex to cause some options to be re- + If the first character following (? is a circumflex, it causes all of + the above options to be unset. Thus, (?^) is equivalent to (?-imnsx). + Letters may follow the circumflex to cause some options to be re- instated, but a hyphen may not appear. - The PCRE2-specific options PCRE2_DUPNAMES and PCRE2_UNGREEDY can be - changed in the same way as the Perl-compatible options by using the + The PCRE2-specific options PCRE2_DUPNAMES and PCRE2_UNGREEDY can be + changed in the same way as the Perl-compatible options by using the characters J and U respectively. However, these are not unset by (?^). - When one of these option changes occurs at top level (that is, not - inside group parentheses), the change applies to the remainder of the - pattern that follows. An option change within a group (see below for a - description of groups) affects only that part of the group that follows - it, so + When one of these option changes occurs at top level (that is, not + inside subpattern parentheses), the change applies to the remainder of + the pattern that follows. An option change within a subpattern (see + below for a description of subpatterns) affects only that part of the + subpattern that follows it, so (a(?i)b)c - matches abc and aBc and no other strings (assuming PCRE2_CASELESS is - not used). By this means, options can be made to have different set- + matches abc and aBc and no other strings (assuming PCRE2_CASELESS is + not used). By this means, options can be made to have different set- tings in different parts of the pattern. Any changes made in one alter- - native do carry on into subsequent branches within the same group. For - example, + native do carry on into subsequent branches within the same subpattern. + For example, (a(?i)b|c) - matches "ab", "aB", "c", and "C", even though when matching "C" the - first branch is abandoned before the option setting. This is because - the effects of option settings happen at compile time. There would be + matches "ab", "aB", "c", and "C", even though when matching "C" the + first branch is abandoned before the option setting. This is because + the effects of option settings happen at compile time. There would be some very weird behaviour otherwise. - As a convenient shorthand, if any option settings are required at the - start of a non-capturing group (see the next section), the option let- - ters may appear between the "?" and the ":". Thus the two patterns + As a convenient shorthand, if any option settings are required at the + start of a non-capturing subpattern (see the next section), the option + letters may appear between the "?" and the ":". Thus the two patterns (?i:saturday|sunday) (?:(?i)saturday|sunday) match exactly the same set of strings. - Note: There are other PCRE2-specific options, applying to the whole - pattern, which can be set by the application when the compiling func- - tion is called. In addition, the pattern can contain special leading - sequences such as (*CRLF) to override what the application has set or - what has been defaulted. Details are given in the section entitled - "Newline sequences" above. There are also the (*UTF) and (*UCP) leading - sequences that can be used to set UTF and Unicode property modes; they - are equivalent to setting the PCRE2_UTF and PCRE2_UCP options, respec- - tively. However, the application can set the PCRE2_NEVER_UTF and - PCRE2_NEVER_UCP options, which lock out the use of the (*UTF) and - (*UCP) sequences. + Note: There are other PCRE2-specific options that can be set by the + application when the compiling function is called. The pattern can con- + tain special leading sequences such as (*CRLF) to override what the + application has set or what has been defaulted. Details are given in + the section entitled "Newline sequences" above. There are also the + (*UTF) and (*UCP) leading sequences that can be used to set UTF and + Unicode property modes; they are equivalent to setting the PCRE2_UTF + and PCRE2_UCP options, respectively. However, the application can set + the PCRE2_NEVER_UTF and PCRE2_NEVER_UCP options, which lock out the use + of the (*UTF) and (*UCP) sequences. -GROUPS +SUBPATTERNS - Groups are delimited by parentheses (round brackets), which can be - nested. Turning part of a pattern into a group does two things: + Subpatterns are delimited by parentheses (round brackets), which can be + nested. Turning part of a pattern into a subpattern does two things: 1. It localizes a set of alternatives. For example, the pattern @@ -7511,53 +7311,55 @@ GROUPS matches "cataract", "caterpillar", or "cat". Without the parentheses, it would match "cataract", "erpillar" or an empty string. - 2. It creates a "capture group". This means that, when the whole pat- - tern matches, the portion of the subject string that matched the group - is passed back to the caller, separately from the portion that matched - the whole pattern. (This applies only to the traditional matching - function; the DFA matching function does not support capturing.) + 2. It sets up the subpattern as a capturing subpattern. This means + that, when the whole pattern matches, the portion of the subject string + that matched the subpattern is passed back to the caller, separately + from the portion that matched the whole pattern. (This applies only to + the traditional matching function; the DFA matching function does not + support capturing.) Opening parentheses are counted from left to right (starting from 1) to - obtain numbers for capture groups. For example, if the string "the red - king" is matched against the pattern + obtain numbers for the capturing subpatterns. For example, if the + string "the red king" is matched against the pattern the ((red|white) (king|queen)) the captured substrings are "red king", "red", and "king", and are num- bered 1, 2, and 3, respectively. - The fact that plain parentheses fulfil two functions is not always - helpful. There are often times when grouping is required without cap- - turing. If an opening parenthesis is followed by a question mark and a - colon, the group does not do any capturing, and is not counted when - computing the number of any subsequent capture groups. For example, if - the string "the white queen" is matched against the pattern + The fact that plain parentheses fulfil two functions is not always + helpful. There are often times when a grouping subpattern is required + without a capturing requirement. If an opening parenthesis is followed + by a question mark and a colon, the subpattern does not do any captur- + ing, and is not counted when computing the number of any subsequent + capturing subpatterns. For example, if the string "the white queen" is + matched against the pattern the ((?:red|white) (king|queen)) the captured substrings are "white queen" and "queen", and are numbered - 1 and 2. The maximum number of capture groups is 65535. + 1 and 2. The maximum number of capturing subpatterns is 65535. As a convenient shorthand, if any option settings are required at the - start of a non-capturing group, the option letters may appear between - the "?" and the ":". Thus the two patterns + start of a non-capturing subpattern, the option letters may appear + between the "?" and the ":". Thus the two patterns (?i:saturday|sunday) (?:(?i)saturday|sunday) match exactly the same set of strings. Because alternative branches are tried from left to right, and options are not reset until the end of - the group is reached, an option setting in one branch does affect sub- - sequent branches, so the above patterns match "SUNDAY" as well as "Sat- - urday". + the subpattern is reached, an option setting in one branch does affect + subsequent branches, so the above patterns match "SUNDAY" as well as + "Saturday". -DUPLICATE GROUP NUMBERS +DUPLICATE SUBPATTERN NUMBERS - Perl 5.10 introduced a feature whereby each alternative in a group uses - the same numbers for its capturing parentheses. Such a group starts - with (?| and is itself a non-capturing group. For example, consider - this pattern: + Perl 5.10 introduced a feature whereby each alternative in a subpattern + uses the same numbers for its capturing parentheses. Such a subpattern + starts with (?| and is itself a non-capturing subpattern. For example, + consider this pattern: (?|(Sat)ur|(Sun))day @@ -7568,7 +7370,7 @@ DUPLICATE GROUP NUMBERS not all, of one of a number of alternatives. Inside a (?| group, paren- theses are numbered as usual, but the number is reset at the start of each branch. The numbers of any capturing parentheses that follow the - whole group start after the highest number used in any branch. The fol- + subpattern start after the highest number used in any branch. The fol- lowing example is taken from the Perl documentation. The numbers under- neath show in which buffer the captured content will be stored. @@ -7576,94 +7378,90 @@ DUPLICATE GROUP NUMBERS / ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x # 1 2 2 3 2 3 4 - A backreference to a capture group uses the most recent value that is - set for the group. The following pattern matches "abcabc" or "defdef": + A backreference to a numbered subpattern uses the most recent value + that is set for that number by any subpattern. The following pattern + matches "abcabc" or "defdef": /(?|(abc)|(def))\1/ - In contrast, a subroutine call to a capture group always refers to the - first one in the pattern with the given number. The following pattern - matches "abcabc" or "defabc": + In contrast, a subroutine call to a numbered subpattern always refers + to the first one in the pattern with the given number. The following + pattern matches "abcabc" or "defabc": /(?|(abc)|(def))(?1)/ A relative reference such as (?-1) is no different: it is just a conve- nient way of computing an absolute group number. - If a condition test for a group's having matched refers to a non-unique - number, the test is true if any group with that number has matched. + If a condition test for a subpattern's having matched refers to a non- + unique number, the test is true if any of the subpatterns of that num- + ber have matched. An alternative approach to using this "branch reset" feature is to use - duplicate named groups, as described in the next section. + duplicate named subpatterns, as described in the next section. -NAMED CAPTURE GROUPS +NAMED SUBPATTERNS - Identifying capture groups by number is simple, but it can be very hard - to keep track of the numbers in complicated patterns. Furthermore, if - an expression is modified, the numbers may change. To help with this - difficulty, PCRE2 supports the naming of capture groups. This feature - was not added to Perl until release 5.10. Python had the feature ear- - lier, and PCRE1 introduced it at release 4.0, using the Python syntax. - PCRE2 supports both the Perl and the Python syntax. + Identifying capturing parentheses by number is simple, but it can be + very hard to keep track of the numbers in complicated patterns. Fur- + thermore, if an expression is modified, the numbers may change. To help + with this difficulty, PCRE2 supports the naming of capturing subpat- + terns. This feature was not added to Perl until release 5.10. Python + had the feature earlier, and PCRE1 introduced it at release 4.0, using + the Python syntax. PCRE2 supports both the Perl and the Python syntax. - In PCRE2, a capture group can be named in one of three ways: + In PCRE2, a capturing subpattern can be named in one of three ways: (?<name>...) or (?'name'...) as in Perl, or (?P<name>...) as in Python. - Names may be up to 32 code units long. When PCRE2_UTF is not set, they - may contain only ASCII alphanumeric characters and underscores, but - must start with a non-digit. When PCRE2_UTF is set, the syntax of group - names is extended to allow any Unicode letter or Unicode decimal digit. - In other words, group names must match one of these patterns: - - ^[_A-Za-z][_A-Za-z0-9]*\z when PCRE2_UTF is not set - ^[_\p{L}][_\p{L}\p{Nd}]*\z when PCRE2_UTF is set - - References to capture groups from other parts of the pattern, such as - backreferences, recursion, and conditions, can all be made by name as - well as by number. - - Named capture groups are allocated numbers as well as names, exactly as - if the names were not present. In both PCRE2 and Perl, capture groups - are primarily identified by numbers; any names are just aliases for - these numbers. The PCRE2 API provides function calls for extracting the - complete name-to-number translation table from a compiled pattern, as - well as convenience functions for extracting captured substrings by - name. - - Warning: When more than one capture group has the same number, as - described in the previous section, a name given to one of them applies - to all of them. Perl allows identically numbered groups to have differ- - ent names. Consider this pattern, where there are two capture groups, - both numbered 1: + Names consist of up to 32 alphanumeric characters and underscores, but + must start with a non-digit. References to capturing parentheses from + other parts of the pattern, such as backreferences, recursion, and con- + ditions, can all be made by name as well as by number. + + Named capturing parentheses are allocated numbers as well as names, + exactly as if the names were not present. In both PCRE2 and Perl, cap- + turing subpatterns are primarily identified by numbers; any names are + just aliases for these numbers. The PCRE2 API provides function calls + for extracting the complete name-to-number translation table from a + compiled pattern, as well as convenience functions for extracting cap- + tured substrings by name. + + Warning: When more than one subpattern has the same number, as + described in the previous section, a name given to one of them applies + to all of them. Perl allows identically numbered subpatterns to have + different names. Consider this pattern, where there are two capturing + subpatterns, both numbered 1: (?|(?<AA>aa)|(?<BB>bb)) - Perl allows this, with both names AA and BB as aliases of group 1. + Perl allows this, with both names AA and BB as aliases of group 1. Thus, after a successful match, both names yield the same value (either "aa" or "bb"). - In an attempt to reduce confusion, PCRE2 does not allow the same group + In an attempt to reduce confusion, PCRE2 does not allow the same group number to be associated with more than one name. The example above pro- - vokes a compile-time error. However, there is still scope for confu- + vokes a compile-time error. However, there is still scope for confu- sion. Consider this pattern: (?|(?<AA>aa)|(bb)) - Although the second group number 1 is not explicitly named, the name AA - is still an alias for any group 1. Whether the pattern matches "aa" or - "bb", a reference by name to group AA yields the matched string. + Although the second subpattern number 1 is not explicitly named, the + name AA is still an alias for subpattern 1. Whether the pattern matches + "aa" or "bb", a reference by name to group AA yields the matched + string. By default, a name must be unique within a pattern, except that dupli- - cate names are permitted for groups with the same number, for example: + cate names are permitted for subpatterns with the same number, for + example: (?|(?<AA>aa)|(?<AA>bb)) The duplicate name constraint can be disabled by setting the PCRE2_DUP- NAMES option at compile time, or by the use of (?J) within the pattern. - Duplicate names can be useful for patterns where only one instance of - the named capture group can match. Suppose you want to match the name - of a weekday, either as a 3-letter abbreviation or as the full name, - and in both cases you want to extract the abbreviation. This pattern + Duplicate names can be useful for patterns where only one instance of + the named parentheses can match. Suppose you want to match the name of + a weekday, either as a 3-letter abbreviation or as the full name, and + in both cases you want to extract the abbreviation. This pattern (ignoring the line breaks) does the job: (?<DN>Mon|Fri|Sun)(?:day)?| @@ -7672,32 +7470,33 @@ NAMED CAPTURE GROUPS (?<DN>Thu)(?:rsday)?| (?<DN>Sat)(?:urday)? - There are five capture groups, but only one is ever set after a match. - The convenience functions for extracting the data by name returns the - substring for the first (and in this example, the only) group of that - name that matched. This saves searching to find which numbered group it - was. (An alternative way of solving this problem is to use a "branch - reset" group, as described in the previous section.) + There are five capturing substrings, but only one is ever set after a + match. The convenience functions for extracting the data by name + returns the substring for the first (and in this example, the only) + subpattern of that name that matched. This saves searching to find + which numbered subpattern it was. (An alternative way of solving this + problem is to use a "branch reset" subpattern, as described in the pre- + vious section.) - If you make a backreference to a non-unique named group from elsewhere - in the pattern, the groups to which the name refers are checked in the - order in which they appear in the overall pattern. The first one that - is set is used for the reference. For example, this pattern matches - both "foofoo" and "barbar" but not "foobar" or "barfoo": + If you make a backreference to a non-unique named subpattern from else- + where in the pattern, the subpatterns to which the name refers are + checked in the order in which they appear in the overall pattern. The + first one that is set is used for the reference. For example, this pat- + tern matches both "foofoo" and "barbar" but not "foobar" or "barfoo": (?:(?<n>foo)|(?<n>bar))\k<n> - If you make a subroutine call to a non-unique named group, the one that - corresponds to the first occurrence of the name is used. In the absence - of duplicate numbers this is the one with the lowest number. + If you make a subroutine call to a non-unique named subpattern, the one + that corresponds to the first occurrence of the name is used. In the + absence of duplicate numbers this is the one with the lowest number. If you use a named reference in a condition test (see the section about - conditions below), either to check whether a capture group has matched, - or to check for recursion, all groups with the same name are tested. If - the condition is true for any one of them, the overall condition is + conditions below), either to check whether a subpattern has matched, or + to check for recursion, all subpatterns with the same name are tested. + If the condition is true for any one of them, the overall condition is true. This is the same behaviour as testing by number. For further - details of the interfaces for handling named capture groups, see the + details of the interfaces for handling named subpatterns, see the pcre2api documentation. @@ -7709,18 +7508,18 @@ REPETITION a literal data character the dot metacharacter the \C escape sequence - the \R escape sequence the \X escape sequence + the \R escape sequence an escape such as \d or \pL that matches a single character a character class a backreference - a parenthesized group (including most assertions) - a subroutine call (recursive or otherwise) + a parenthesized subpattern (including most assertions) + a subroutine call to a subpattern (recursive or otherwise) The general repetition quantifier specifies a minimum and maximum num- ber of permitted matches, by giving the two numbers in curly brackets (braces), separated by a comma. The numbers must be less than 65536, - and the first must be less than or equal to the second. For example, + and the first must be less than or equal to the second. For example: z{2,4} @@ -7750,34 +7549,34 @@ REPETITION The quantifier {0} is permitted, causing the expression to behave as if the previous item and the quantifier were not present. This may be use- - ful for capture groups that are referenced as subroutines from else- - where in the pattern (but see also the section entitled "Defining cap- - ture groups for use by reference only" below). Except for parenthesized - groups, items that have a {0} quantifier are omitted from the compiled - pattern. + ful for subpatterns that are referenced as subroutines from elsewhere + in the pattern (but see also the section entitled "Defining subpatterns + for use by reference only" below). Items other than subpatterns that + have a {0} quantifier are omitted from the compiled pattern. - For convenience, the three most common quantifiers have single-charac- + For convenience, the three most common quantifiers have single-charac- ter abbreviations: * is equivalent to {0,} + is equivalent to {1,} ? is equivalent to {0,1} - It is possible to construct infinite loops by following a group that - can match no characters with a quantifier that has no upper limit, for - example: + It is possible to construct infinite loops by following a subpattern + that can match no characters with a quantifier that has no upper limit, + for example: (a?)* - Earlier versions of Perl and PCRE1 used to give an error at compile + Earlier versions of Perl and PCRE1 used to give an error at compile time for such patterns. However, because there are cases where this can be useful, such patterns are now accepted, but if any repetition of the - group does in fact match no characters, the loop is forcibly broken. + subpattern does in fact match no characters, the loop is forcibly bro- + ken. - By default, quantifiers are "greedy", that is, they match as much as - possible (up to the maximum number of permitted times), without causing - the rest of the pattern to fail. The classic example of where this - gives problems is in trying to match comments in C programs. These + By default, the quantifiers are "greedy", that is, they match as much + as possible (up to the maximum number of permitted times), without + causing the rest of the pattern to fail. The classic example of where + this gives problems is in trying to match comments in C programs. These appear between /* and */ and within the comment, individual * and / characters may appear. An attempt to match C comments by applying the pattern @@ -7789,9 +7588,11 @@ REPETITION /* first comment */ not comment /* second comment */ fails, because it matches the entire string owing to the greediness of - the .* item. However, if a quantifier is followed by a question mark, - it ceases to be greedy, and instead matches the minimum number of times - possible, so the pattern + the .* item. + + If a quantifier is followed by a question mark, it ceases to be greedy, + and instead matches the minimum number of times possible, so the pat- + tern /\*.*?\*/ @@ -7811,8 +7612,8 @@ REPETITION can be made greedy by following them with a question mark. In other words, it inverts the default behaviour. - When a parenthesized group is quantified with a minimum repeat count - that is greater than 1 or with a limited maximum, more memory is + When a parenthesized subpattern is quantified with a minimum repeat + count that is greater than 1 or with a limited maximum, more memory is required for the compiled pattern, in proportion to the size of the minimum or maximum. @@ -7848,15 +7649,15 @@ REPETITION trol verbs (*PRUNE) and (*SKIP) also disable this optimization, and there is an option, PCRE2_NO_DOTSTAR_ANCHOR, to do so explicitly. - When a capture group is repeated, the value captured is the substring - that matched the final iteration. For example, after + When a capturing subpattern is repeated, the value captured is the sub- + string that matched the final iteration. For example, after (tweedle[dume]{3}\s*)+ has matched "tweedledum tweedledee" the value of the captured substring - is "tweedledee". However, if there are nested capture groups, the cor- - responding captured values may have been set in previous iterations. - For example, after + is "tweedledee". However, if there are nested capturing subpatterns, + the corresponding captured values may have been set in previous itera- + tions. For example, after (a|(b))+ @@ -7882,8 +7683,8 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS action of the matcher is to try again with only 5 digits matching the \d+ item, and then with 4, and so on, before ultimately failing. "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides - the means for specifying that once a group has matched, it is not to be - re-evaluated in this way. + the means for specifying that once a subpattern has matched, it is not + to be re-evaluated in this way. If we use atomic grouping for the previous example, the matcher gives up immediately on failing to match "foo" the first time. The notation @@ -7891,32 +7692,28 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS (?>\d+)foo - Perl 5.28 introduced an experimental alphabetic form starting with (* - which may be easier to remember: - - (*atomic:\d+)foo - - This kind of parenthesized group "locks up" the part of the pattern it - contains once it has matched, and a failure further into the pattern is - prevented from backtracking into it. Backtracking past it to previous + This kind of parenthesis "locks up" the part of the pattern it con- + tains once it has matched, and a failure further into the pattern is + prevented from backtracking into it. Backtracking past it to previous items, however, works as normal. - An alternative description is that a group of this type matches exactly - the string of characters that an identical standalone pattern would - match, if anchored at the current point in the subject string. + An alternative description is that a subpattern of this type matches + exactly the string of characters that an identical standalone pattern + would match, if anchored at the current point in the subject string. - Atomic groups are not capture groups. Simple cases such as the above - example can be thought of as a maximizing repeat that must swallow - everything it can. So, while both \d+ and \d+? are prepared to adjust - the number of digits they match in order to make the rest of the pat- - tern match, (?>\d+) can only match an entire sequence of digits. + Atomic grouping subpatterns are not capturing subpatterns. Simple cases + such as the above example can be thought of as a maximizing repeat that + must swallow everything it can. So, while both \d+ and \d+? are pre- + pared to adjust the number of digits they match in order to make the + rest of the pattern match, (?>\d+) can only match an entire sequence of + digits. Atomic groups in general can of course contain arbitrarily complicated - expressions, and can be nested. However, when the contents of an atomic - group is just a single repeated item, as in the example above, a sim- - pler notation, called a "possessive quantifier" can be used. This con- - sists of an additional + character following a quantifier. Using this - notation, the previous example can be rewritten as + subpatterns, and can be nested. However, when the subpattern for an + atomic group is just a single repeated item, as in the example above, a + simpler notation, called a "possessive quantifier" can be used. This + consists of an additional + character following a quantifier. Using + this notation, the previous example can be rewritten as \d++foo @@ -7935,8 +7732,8 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS The possessive quantifier syntax is an extension to the Perl 5.8 syn- tax. Jeffrey Friedl originated the idea (and the name) in the first edition of his book. Mike McCloskey liked it, so implemented it when he - built Sun's Java package, and PCRE1 copied it from there. It found its - way into Perl at release 5.10. + built Sun's Java package, and PCRE1 copied it from there. It ultimately + found its way into Perl at release 5.10. PCRE2 has an optimization that automatically "possessifies" certain simple pattern constructs. For example, the sequence A+B is treated as @@ -7944,10 +7741,10 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS when B must follow. This feature can be disabled by the PCRE2_NO_AUTO- POSSESS option, or starting the pattern with (*NO_AUTO_POSSESS). - When a pattern contains an unlimited repeat inside a group that can - itself be repeated an unlimited number of times, the use of an atomic - group is the only way to avoid some failing matches taking a very long - time indeed. The pattern + When a pattern contains an unlimited repeat inside a subpattern that + can itself be repeated an unlimited number of times, the use of an + atomic group is the only way to avoid some failing matches taking a + very long time indeed. The pattern (\D+|<\d+>)*[!?] @@ -7975,28 +7772,29 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS BACKREFERENCES Outside a character class, a backslash followed by a digit greater than - 0 (and possibly further digits) is a backreference to a capture group - earlier (that is, to its left) in the pattern, provided there have been - that many previous capture groups. + 0 (and possibly further digits) is a backreference to a capturing sub- + pattern earlier (that is, to its left) in the pattern, provided there + have been that many previous capturing left parentheses. However, if the decimal number following the backslash is less than 8, it is always taken as a backreference, and causes an error only if - there are not that many capture groups in the entire pattern. In other - words, the group that is referenced need not be to the left of the ref- - erence for numbers less than 8. A "forward backreference" of this type - can make sense when a repetition is involved and the group to the right - has participated in an earlier iteration. - - It is not possible to have a numerical "forward backreference" to a - group whose number is 8 or more using this syntax because a sequence - such as \50 is interpreted as a character defined in octal. See the - subsection entitled "Non-printing characters" above for further details - of the handling of digits following a backslash. Other forms of back- - referencing do not suffer from this restriction. In particular, there - is no problem when named capture groups are used (see below). - - Another way of avoiding the ambiguity inherent in the use of digits - following a backslash is to use the \g escape sequence. This escape + there are not that many capturing left parentheses in the entire pat- + tern. In other words, the parentheses that are referenced need not be + to the left of the reference for numbers less than 8. A "forward back- + reference" of this type can make sense when a repetition is involved + and the subpattern to the right has participated in an earlier itera- + tion. + + It is not possible to have a numerical "forward backreference" to a + subpattern whose number is 8 or more using this syntax because a + sequence such as \50 is interpreted as a character defined in octal. + See the subsection entitled "Non-printing characters" above for further + details of the handling of digits following a backslash. There is no + such problem when named parentheses are used. A backreference to any + subpattern is possible using named parentheses (see below). + + Another way of avoiding the ambiguity inherent in the use of digits + following a backslash is to use the \g escape sequence. This escape must be followed by a signed or unsigned number, optionally enclosed in braces. These examples are all identical: @@ -8004,85 +7802,86 @@ BACKREFERENCES (ring), \g1 (ring), \g{1} - An unsigned number specifies an absolute reference without the ambigu- + An unsigned number specifies an absolute reference without the ambigu- ity that is present in the older syntax. It is also useful when literal - digits follow the reference. A signed number is a relative reference. + digits follow the reference. A signed number is a relative reference. Consider this example: (abc(def)ghi)\g{-1} - The sequence \g{-1} is a reference to the most recently started capture - group before \g, that is, is it equivalent to \2 in this example. Simi- - larly, \g{-2} would be equivalent to \1. The use of relative references - can be helpful in long patterns, and also in patterns that are created - by joining together fragments that contain references within them- - selves. + The sequence \g{-1} is a reference to the most recently started captur- + ing subpattern before \g, that is, is it equivalent to \2 in this exam- + ple. Similarly, \g{-2} would be equivalent to \1. The use of relative + references can be helpful in long patterns, and also in patterns that + are created by joining together fragments that contain references + within themselves. - The sequence \g{+1} is a reference to the next capture group. This kind - of forward reference can be useful in patterns that repeat. Perl does - not support the use of + in this way. + The sequence \g{+1} is a reference to the next capturing subpattern. + This kind of forward reference can be useful it patterns that repeat. + Perl does not support the use of + in this way. - A backreference matches whatever actually most recently matched the - capture group in the current subject string, rather than anything at - all that matches the group (see "Groups as subroutines" below for a way - of doing that). So the pattern + A backreference matches whatever actually matched the capturing subpat- + tern in the current subject string, rather than anything matching the + subpattern itself (see "Subpatterns as subroutines" below for a way of + doing that). So the pattern (sens|respons)e and \1ibility - matches "sense and sensibility" and "response and responsibility", but - not "sense and responsibility". If caseful matching is in force at the - time of the backreference, the case of letters is relevant. For exam- + matches "sense and sensibility" and "response and responsibility", but + not "sense and responsibility". If caseful matching is in force at the + time of the backreference, the case of letters is relevant. For exam- ple, ((?i)rah)\s+\1 - matches "rah rah" and "RAH RAH", but not "RAH rah", even though the - original capture group is matched caselessly. + matches "rah rah" and "RAH RAH", but not "RAH rah", even though the + original capturing subpattern is matched caselessly. - There are several different ways of writing backreferences to named - capture groups. The .NET syntax \k{name} and the Perl syntax \k<name> - or \k'name' are supported, as is the Python syntax (?P=name). Perl - 5.10's unified backreference syntax, in which \g can be used for both - numeric and named references, is also supported. We could rewrite the - above example in any of the following ways: + There are several different ways of writing backreferences to named + subpatterns. The .NET syntax \k{name} and the Perl syntax \k<name> or + \k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's + unified backreference syntax, in which \g can be used for both numeric + and named references, is also supported. We could rewrite the above + example in any of the following ways: (?<p1>(?i)rah)\s+\k<p1> (?'p1'(?i)rah)\s+\k{p1} (?P<p1>(?i)rah)\s+(?P=p1) (?<p1>(?i)rah)\s+\g{p1} - A capture group that is referenced by name may appear in the pattern + A subpattern that is referenced by name may appear in the pattern before or after the reference. - There may be more than one backreference to the same group. If a group - has not actually been used in a particular match, backreferences to it - always fail by default. For example, the pattern + There may be more than one backreference to the same subpattern. If a + subpattern has not actually been used in a particular match, any back- + references to it always fail by default. For example, the pattern (a|(bc))\2 - always fails if it starts to match "a" rather than "bc". However, if + always fails if it starts to match "a" rather than "bc". However, if the PCRE2_MATCH_UNSET_BACKREF option is set at compile time, a backref- erence to an unset value matches an empty string. - Because there may be many capture groups in a pattern, all digits fol- - lowing a backslash are taken as part of a potential backreference num- - ber. If the pattern continues with a digit character, some delimiter - must be used to terminate the backreference. If the PCRE2_EXTENDED or - PCRE2_EXTENDED_MORE option is set, this can be white space. Otherwise, - the \g{} syntax or an empty comment (see "Comments" below) can be used. + Because there may be many capturing parentheses in a pattern, all dig- + its following a backslash are taken as part of a potential backrefer- + ence number. If the pattern continues with a digit character, some + delimiter must be used to terminate the backreference. If the + PCRE2_EXTENDED or PCRE2_EXTENDED_MORE option is set, this can be white + space. Otherwise, the \g{ syntax or an empty comment (see "Comments" + below) can be used. Recursive backreferences - A backreference that occurs inside the group to which it refers fails - when the group is first used, so, for example, (a\1) never matches. - However, such references can be useful inside repeated groups. For - example, the pattern + A backreference that occurs inside the parentheses to which it refers + fails when the subpattern is first used, so, for example, (a\1) never + matches. However, such references can be useful inside repeated sub- + patterns. For example, the pattern (a|b\1)+ matches any number of "a"s and also "aba", "ababbaa" etc. At each iter- - ation of the group, the backreference matches the character string cor- - responding to the previous iteration. In order for this to work, the + ation of the subpattern, the backreference matches the character string + corresponding to the previous iteration. In order for this to work, the pattern must be such that the first iteration does not need to match the backreference. This can be done using alternation, as in the exam- ple above, or by a quantifier with a minimum of zero. @@ -8100,29 +7899,25 @@ ASSERTIONS assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are described above. - More complicated assertions are coded as parenthesized groups. There - are two kinds: those that look ahead of the current position in the - subject string, and those that look behind it, and in each case an - assertion may be positive (must match for the assertion to be true) or - negative (must not match for the assertion to be true). An assertion - group is matched in the normal way, and if it is true, matching contin- - ues after it, but with the matching position in the subject string is - was it was before the assertion was processed. - - A lookaround assertion may also appear as the condition in a condi- - tional group (see below). In this case, the result of matching the - assertion determines which branch of the condition is followed. - - Assertion groups are not capture groups. If an assertion contains cap- - ture groups within it, these are counted for the purposes of numbering - the capture groups in the whole pattern. Within each branch of an - assertion, locally captured substrings may be referenced in the usual - way. For example, a sequence such as (.)\g{-1} can be used to check - that two adjacent characters are the same. + More complicated assertions are coded as subpatterns. There are two + kinds: those that look ahead of the current position in the subject + string, and those that look behind it, and in each case an assertion + may be positive (must succeed for matching to continue) or negative + (must not succeed for matching to continue). An assertion subpattern is + matched in the normal way, except that, when matching continues after a + successful assertion, the matching position in the subject string is as + it was before the assertion was processed. + + Assertion subpatterns are not capturing subpatterns. If an assertion + contains capturing subpatterns within it, these are counted for the + purposes of numbering the capturing subpatterns in the whole pattern. + Within each branch of an assertion, locally captured substrings may be + referenced in the usual way. For example, a sequence such as (.)\g{-1} + can be used to check that two adjacent characters are the same. When a branch within an assertion fails to match, any substrings that were captured are discarded (as happens with any pattern branch that - fails to match). A negative assertion is true only when all its + fails to match). A negative assertion succeeds only when all its branches fail to match; this means that no captured substrings are ever retained after a successful negative assertion. When an assertion con- tains a matching branch, what happens depends on the type of assertion. @@ -8130,49 +7925,33 @@ ASSERTIONS For a positive assertion, internally captured substrings in the suc- cessful branch are retained, and matching continues with the next pat- tern item after the assertion. For a negative assertion, a matching - branch means that the assertion is not true. If such an assertion is - being used as a condition in a conditional group (see below), captured + branch means that the assertion has failed. If the assertion is being + used as a condition in a conditional subpattern (see below), captured substrings are retained, because matching continues with the "no" branch of the condition. For other failing negative assertions, control passes to the previous backtracking point, thus discarding any captured strings within the assertion. - For compatibility with Perl, most assertion groups may be repeated; - though it makes no sense to assert the same thing several times, the - side effect of capturing may occasionally be useful. However, an asser- - tion that forms the condition for a conditional group may not be quan- - tified. In practice, for other assertions, there only three cases: + For compatibility with Perl, most assertion subpatterns may be + repeated; though it makes no sense to assert the same thing several + times, the side effect of capturing parentheses may occasionally be + useful. However, an assertion that forms the condition for a condi- + tional subpattern may not be quantified. In practice, for other asser- + tions, there only three cases: - (1) If the quantifier is {0}, the assertion is never obeyed during - matching. However, it may contain internal capture groups that are - called from elsewhere via the subroutine mechanism. + (1) If the quantifier is {0}, the assertion is never obeyed during + matching. However, it may contain internal capturing parenthesized + groups that are called from elsewhere via the subroutine mechanism. - (2) If quantifier is {0,n} where n is greater than zero, it is treated - as if it were {0,1}. At run time, the rest of the pattern match is + (2) If quantifier is {0,n} where n is greater than zero, it is treated + as if it were {0,1}. At run time, the rest of the pattern match is tried with and without the assertion, the order depending on the greed- iness of the quantifier. - (3) If the minimum repetition is greater than zero, the quantifier is - ignored. The assertion is obeyed just once when encountered during + (3) If the minimum repetition is greater than zero, the quantifier is + ignored. The assertion is obeyed just once when encountered during matching. - Alphabetic assertion names - - Traditionally, symbolic sequences such as (?= and (?<= have been used - to specify lookaround assertions. Perl 5.28 introduced some experimen- - tal alphabetic alternatives which might be easier to remember. They all - start with (* instead of (? and must be written using lower case let- - ters. PCRE2 supports the following synonyms: - - (*positive_lookahead: or (*pla: is the same as (?= - (*negative_lookahead: or (*nla: is the same as (?! - (*positive_lookbehind: or (*plb: is the same as (?<= - (*negative_lookbehind: or (*nlb: is the same as (?<! - - For example, (*pla:foo) is the same assertion as (?=foo). In the fol- - lowing sections, the various assertions are described using the origi- - nal symbolic forms. - Lookahead assertions Lookahead assertions start with (?= for positive assertions and (?! for @@ -8180,38 +7959,38 @@ ASSERTIONS \w+(?=;) - matches a word followed by a semicolon, but does not include the semi- + matches a word followed by a semicolon, but does not include the semi- colon in the match, and foo(?!bar) - matches any occurrence of "foo" that is not followed by "bar". Note + matches any occurrence of "foo" that is not followed by "bar". Note that the apparently similar pattern (?!foo)bar - does not find an occurrence of "bar" that is preceded by something - other than "foo"; it finds any occurrence of "bar" whatsoever, because + does not find an occurrence of "bar" that is preceded by something + other than "foo"; it finds any occurrence of "bar" whatsoever, because the assertion (?!foo) is always true when the next three characters are "bar". A lookbehind assertion is needed to achieve the other effect. If you want to force a matching failure at some point in a pattern, the - most convenient way to do it is with (?!) because an empty string - always matches, so an assertion that requires there not to be an empty + most convenient way to do it is with (?!) because an empty string + always matches, so an assertion that requires there not to be an empty string must always fail. The backtracking control verb (*FAIL) or (*F) is a synonym for (?!). Lookbehind assertions - Lookbehind assertions start with (?<= for positive assertions and (?<! + Lookbehind assertions start with (?<= for positive assertions and (?<! for negative assertions. For example, (?<!foo)bar - does find an occurrence of "bar" that is not preceded by "foo". The - contents of a lookbehind assertion are restricted such that all the + does find an occurrence of "bar" that is not preceded by "foo". The + contents of a lookbehind assertion are restricted such that all the strings it matches must have a fixed length. However, if there are sev- - eral top-level alternatives, they do not all have to have the same + eral top-level alternatives, they do not all have to have the same fixed length. Thus (?<=bullock|donkey) @@ -8220,74 +7999,74 @@ ASSERTIONS (?<!dogs?|cats?) - causes an error at compile time. Branches that match different length - strings are permitted only at the top level of a lookbehind assertion. + causes an error at compile time. Branches that match different length + strings are permitted only at the top level of a lookbehind assertion. This is an extension compared with Perl, which requires all branches to match the same length of string. An assertion such as (?<=ab(c|de)) - is not permitted, because its single top-level branch can match two - different lengths, but it is acceptable to PCRE2 if rewritten to use + is not permitted, because its single top-level branch can match two + different lengths, but it is acceptable to PCRE2 if rewritten to use two top-level branches: (?<=abc|abde) - In some cases, the escape sequence \K (see above) can be used instead + In some cases, the escape sequence \K (see above) can be used instead of a lookbehind assertion to get round the fixed-length restriction. - The implementation of lookbehind assertions is, for each alternative, - to temporarily move the current position back by the fixed length and + The implementation of lookbehind assertions is, for each alternative, + to temporarily move the current position back by the fixed length and then try to match. If there are insufficient characters before the cur- rent position, the assertion fails. - In UTF-8 and UTF-16 modes, PCRE2 does not allow the \C escape (which - matches a single code unit even in a UTF mode) to appear in lookbehind - assertions, because it makes it impossible to calculate the length of - the lookbehind. The \X and \R escapes, which can match different num- + In UTF-8 and UTF-16 modes, PCRE2 does not allow the \C escape (which + matches a single code unit even in a UTF mode) to appear in lookbehind + assertions, because it makes it impossible to calculate the length of + the lookbehind. The \X and \R escapes, which can match different num- bers of code units, are never permitted in lookbehinds. - "Subroutine" calls (see below) such as (?2) or (?&X) are permitted in - lookbehinds, as long as the called capture group matches a fixed-length - string. However, recursion, that is, a "subroutine" call into a group - that is already active, is not supported. + "Subroutine" calls (see below) such as (?2) or (?&X) are permitted in + lookbehinds, as long as the subpattern matches a fixed-length string. + However, recursion, that is, a "subroutine" call into a group that is + already active, is not supported. Perl does not support backreferences in lookbehinds. PCRE2 does support - them, but only if certain conditions are met. The - PCRE2_MATCH_UNSET_BACKREF option must not be set, there must be no use - of (?| in the pattern (it creates duplicate group numbers), and if the - backreference is by name, the name must be unique. Of course, the ref- - erenced group must itself match a fixed length substring. The following + them, but only if certain conditions are met. The + PCRE2_MATCH_UNSET_BACKREF option must not be set, there must be no use + of (?| in the pattern (it creates duplicate subpattern numbers), and if + the backreference is by name, the name must be unique. Of course, the + referenced subpattern must itself be of fixed length. The following pattern matches words containing at least two characters that begin and end with the same character: \b(\w)\w++(?<=\1) - Possessive quantifiers can be used in conjunction with lookbehind + Possessive quantifiers can be used in conjunction with lookbehind assertions to specify efficient matching of fixed-length strings at the end of subject strings. Consider a simple pattern such as abcd$ - when applied to a long string that does not match. Because matching - proceeds from left to right, PCRE2 will look for each "a" in the sub- - ject and then see if what follows matches the rest of the pattern. If + when applied to a long string that does not match. Because matching + proceeds from left to right, PCRE2 will look for each "a" in the sub- + ject and then see if what follows matches the rest of the pattern. If the pattern is specified as ^.*abcd$ - the initial .* matches the entire string at first, but when this fails + the initial .* matches the entire string at first, but when this fails (because there is no following "a"), it backtracks to match all but the - last character, then all but the last two characters, and so on. Once - again the search for "a" covers the entire string, from right to left, + last character, then all but the last two characters, and so on. Once + again the search for "a" covers the entire string, from right to left, so we are no better off. However, if the pattern is written as ^.*+(?<=abcd) there can be no backtracking for the .*+ item because of the possessive quantifier; it can match only the entire string. The subsequent lookbe- - hind assertion does a single test on the last four characters. If it - fails, the match fails immediately. For long strings, this approach + hind assertion does a single test on the last four characters. If it + fails, the match fails immediately. For long strings, this approach makes a significant difference to the processing time. Using multiple assertions @@ -8296,18 +8075,18 @@ ASSERTIONS (?<=\d{3})(?<!999)foo - matches "foo" preceded by three digits that are not "999". Notice that - each of the assertions is applied independently at the same point in - the subject string. First there is a check that the previous three - characters are all digits, and then there is a check that the same + matches "foo" preceded by three digits that are not "999". Notice that + each of the assertions is applied independently at the same point in + the subject string. First there is a check that the previous three + characters are all digits, and then there is a check that the same three characters are not "999". This pattern does not match "foo" pre- - ceded by six characters, the first of which are digits and the last - three of which are not "999". For example, it doesn't match "123abc- + ceded by six characters, the first of which are digits and the last + three of which are not "999". For example, it doesn't match "123abc- foo". A pattern to do that is (?<=\d{3}...)(?<!999)foo - This time the first assertion looks at the preceding six characters, + This time the first assertion looks at the preceding six characters, checking that the first three are digits, and then the second assertion checks that the preceding three characters are not "999". @@ -8315,77 +8094,22 @@ ASSERTIONS (?<=(?<!foo)bar)baz - matches an occurrence of "baz" that is preceded by "bar" which in turn + matches an occurrence of "baz" that is preceded by "bar" which in turn is not preceded by "foo", while (?<=\d{3}(?!999)...)foo - is another pattern that matches "foo" preceded by three digits and any + is another pattern that matches "foo" preceded by three digits and any three characters that are not "999". -SCRIPT RUNS - - In concept, a script run is a sequence of characters that are all from - the same Unicode script such as Latin or Greek. However, because some - scripts are commonly used together, and because some diacritical and - other marks are used with multiple scripts, it is not that simple. - There is a full description of the rules that PCRE2 uses in the section - entitled "Script Runs" in the pcre2unicode documentation. - - If part of a pattern is enclosed between (*script_run: or (*sr: and a - closing parenthesis, it fails if the sequence of characters that it - matches are not a script run. After a failure, normal backtracking - occurs. Script runs can be used to detect spoofing attacks using char- - acters that look the same, but are from different scripts. The string - "paypal.com" is an infamous example, where the letters could be a mix- - ture of Latin and Cyrillic. This pattern ensures that the matched char- - acters in a sequence of non-spaces that follow white space are a script - run: - - \s+(*sr:\S+) - - To be sure that they are all from the Latin script (for example), a - lookahead can be used: - - \s+(?=\p{Latin})(*sr:\S+) - - This works as long as the first character is expected to be a character - in that script, and not (for example) punctuation, which is allowed - with any script. If this is not the case, a more creative lookahead is - needed. For example, if digits, underscore, and dots are permitted at - the start: - - \s+(?=[0-9_.]*\p{Latin})(*sr:\S+) - - - In many cases, backtracking into a script run pattern fragment is not - desirable. The script run can employ an atomic group to prevent this. - Because this is a common requirement, a shorthand notation is provided - by (*atomic_script_run: or (*asr: - - (*asr:...) is the same as (*sr:(?>...)) - - Note that the atomic group is inside the script run. Putting it outside - would not prevent backtracking into the script run pattern. +CONDITIONAL SUBPATTERNS - Support for script runs is not available if PCRE2 is compiled without - Unicode support. A compile-time error is given if any of the above con- - structs is encountered. Script runs are not supported by the alternate - matching function, pcre2_dfa_match() because they use the same mecha- - nism as capturing parentheses. - - Warning: The (*ACCEPT) control verb (see below) should not be used - within a script run group, because it causes an immediate exit from the - group, bypassing the script run checking. - - -CONDITIONAL GROUPS - - It is possible to cause the matching process to obey a pattern fragment - conditionally or to choose between two alternative fragments, depending - on the result of an assertion, or whether a specific capture group has - already been matched. The two possible forms of conditional group are: + It is possible to cause the matching process to obey a subpattern con- + ditionally or to choose between two alternative subpatterns, depending + on the result of an assertion, or whether a specific capturing subpat- + tern has already been matched. The two possible forms of conditional + subpattern are: (?(condition)yes-pattern) (?(condition)yes-pattern|no-pattern) @@ -8393,33 +8117,33 @@ CONDITIONAL GROUPS If the condition is satisfied, the yes-pattern is used; otherwise the no-pattern (if present) is used. An absent no-pattern is equivalent to an empty string (it always matches). If there are more than two alter- - natives in the group, a compile-time error occurs. Each of the two - alternatives may itself contain nested groups of any form, including - conditional groups; the restriction to two alternatives applies only at - the level of the condition itself. This pattern fragment is an example - where the alternatives are complex: + natives in the subpattern, a compile-time error occurs. Each of the two + alternatives may itself contain nested subpatterns of any form, includ- + ing conditional subpatterns; the restriction to two alternatives + applies only at the level of the condition. This pattern fragment is an + example where the alternatives are complex: (?(1) (A|B|C) | (D | (?(2)E|F) | E) ) - There are five kinds of condition: references to capture groups, refer- + There are five kinds of condition: references to subpatterns, refer- ences to recursion, two pseudo-conditions called DEFINE and VERSION, and assertions. - Checking for a used capture group by number + Checking for a used subpattern by number If the text between the parentheses consists of a sequence of digits, - the condition is true if a capture group of that number has previously - matched. If there is more than one capture group with the same number - (see the earlier section about duplicate group numbers), the condition - is true if any of them have matched. An alternative notation is to pre- - cede the digits with a plus or minus sign. In this case, the group num- - ber is relative rather than absolute. The most recently opened capture - group can be referenced by (?(-1), the next most recent by (?(-2), and - so on. Inside loops it can also make sense to refer to subsequent - groups. The next capture group can be referenced as (?(+1), and so on. - (The value zero in any of these forms is not used; it provokes a com- - pile-time error.) + the condition is true if a capturing subpattern of that number has pre- + viously matched. If there is more than one capturing subpattern with + the same number (see the earlier section about duplicate subpattern + numbers), the condition is true if any of them have matched. An alter- + native notation is to precede the digits with a plus or minus sign. In + this case, the subpattern number is relative rather than absolute. The + most recently opened parentheses can be referenced by (?(-1), the next + most recent by (?(-2), and so on. Inside loops it can also make sense + to refer to subsequent groups. The next parentheses to be opened can be + referenced as (?(+1), and so on. (The value zero in any of these forms + is not used; it provokes a compile-time error.) Consider the following pattern, which contains non-significant white space to make it more readable (assume the PCRE2_EXTENDED option) and @@ -8430,13 +8154,13 @@ CONDITIONAL GROUPS The first part matches an optional opening parenthesis, and if that character is present, sets it as the first captured substring. The sec- ond part matches one or more characters that are not parentheses. The - third part is a conditional group that tests whether or not the first - capture group matched. If it did, that is, if subject started with an - opening parenthesis, the condition is true, and so the yes-pattern is - executed and a closing parenthesis is required. Otherwise, since no- - pattern is not present, the conditional group matches nothing. In other - words, this pattern matches a sequence of non-parentheses, optionally - enclosed in parentheses. + third part is a conditional subpattern that tests whether or not the + first set of parentheses matched. If they did, that is, if subject + started with an opening parenthesis, the condition is true, and so the + yes-pattern is executed and a closing parenthesis is required. Other- + wise, since no-pattern is not present, the subpattern matches nothing. + In other words, this pattern matches a sequence of non-parentheses, + optionally enclosed in parentheses. If you were embedding this pattern in a larger one, you could use a relative reference: @@ -8446,104 +8170,104 @@ CONDITIONAL GROUPS This makes the fragment independent of the parentheses in the larger pattern. - Checking for a used capture group by name + Checking for a used subpattern by name Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a - used capture group by name. For compatibility with earlier versions of + used subpattern by name. For compatibility with earlier versions of PCRE1, which had this facility before Perl, the syntax (?(name)...) is - also recognized. Note, however, that undelimited names consisting of + also recognized. Note, however, that undelimited names consisting of the letter R followed by digits are ambiguous (see the following sec- - tion). Rewriting the above example to use a named group gives this: + tion). + + Rewriting the above example to use a named subpattern gives this: (?<OPEN> \( )? [^()]+ (?(<OPEN>) \) ) If the name used in a condition of this kind is a duplicate, the test - is applied to all groups of the same name, and is true if any one of - them has matched. + is applied to all subpatterns of the same name, and is true if any one + of them has matched. Checking for pattern recursion "Recursion" in this sense refers to any subroutine-like call from one part of the pattern to another, whether or not it is actually recur- - sive. See the sections entitled "Recursive patterns" and "Groups as - subroutines" below for details of recursion and subroutine calls. - - If a condition is the string (R), and there is no capture group with - the name R, the condition is true if matching is currently in a recur- - sion or subroutine call to the whole pattern or any capture group. If - digits follow the letter R, and there is no group with that name, the - condition is true if the most recent call is into a group with the + sive. See the sections entitled "Recursive patterns" and "Subpatterns + as subroutines" below for details of recursion and subpattern calls. + + If a condition is the string (R), and there is no subpattern with the + name R, the condition is true if matching is currently in a recursion + or subroutine call to the whole pattern or any subpattern. If digits + follow the letter R, and there is no subpattern with that name, the + condition is true if the most recent call is into a subpattern with the given number, which must exist somewhere in the overall pattern. This is a contrived example that is equivalent to a+b: ((?(R1)a+|(?1)b)) - However, in both cases, if there is a capture group with a matching - name, the condition tests for its being set, as described in the sec- - tion above, instead of testing for recursion. For example, creating a - group with the name R1 by adding (?<R1>) to the above pattern com- - pletely changes its meaning. + However, in both cases, if there is a subpattern with a matching name, + the condition tests for its being set, as described in the section + above, instead of testing for recursion. For example, creating a group + with the name R1 by adding (?<R1>) to the above pattern completely + changes its meaning. If a name preceded by ampersand follows the letter R, for example: (?(R&name)...) - the condition is true if the most recent recursion is into a group of - that name (which must exist within the pattern). + the condition is true if the most recent recursion is into a subpattern + of that name (which must exist within the pattern). This condition does not check the entire recursion stack. It tests only the current level. If the name used in a condition of this kind is a - duplicate, the test is applied to all groups of the same name, and is - true if any one of them is the most recent recursion. + duplicate, the test is applied to all subpatterns of the same name, and + is true if any one of them is the most recent recursion. At "top level", all these recursion test conditions are false. - Defining capture groups for use by reference only + Defining subpatterns for use by reference only If the condition is the string (DEFINE), the condition is always false, even if there is a group with the name DEFINE. In this case, there may - be only one alternative in the rest of the conditional group. It is - always skipped if control reaches this point in the pattern; the idea - of DEFINE is that it can be used to define subroutines that can be ref- - erenced from elsewhere. (The use of subroutines is described below.) - For example, a pattern to match an IPv4 address such as - "192.168.23.245" could be written like this (ignore white space and - line breaks): + be only one alternative in the subpattern. It is always skipped if con- + trol reaches this point in the pattern; the idea of DEFINE is that it + can be used to define subroutines that can be referenced from else- + where. (The use of subroutines is described below.) For example, a pat- + tern to match an IPv4 address such as "192.168.23.245" could be written + like this (ignore white space and line breaks): (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) ) \b (?&byte) (\.(?&byte)){3} \b - The first part of the pattern is a DEFINE group inside which a another - group named "byte" is defined. This matches an individual component of - an IPv4 address (a number less than 256). When matching takes place, - this part of the pattern is skipped because DEFINE acts like a false - condition. The rest of the pattern uses references to the named group - to match the four dot-separated components of an IPv4 address, insist- + The first part of the pattern is a DEFINE group inside which a another + group named "byte" is defined. This matches an individual component of + an IPv4 address (a number less than 256). When matching takes place, + this part of the pattern is skipped because DEFINE acts like a false + condition. The rest of the pattern uses references to the named group + to match the four dot-separated components of an IPv4 address, insist- ing on a word boundary at each end. Checking the PCRE2 version - Programs that link with a PCRE2 library can check the version by call- - ing pcre2_config() with appropriate arguments. Users of applications - that do not have access to the underlying code cannot do this. A spe- - cial "condition" called VERSION exists to allow such users to discover + Programs that link with a PCRE2 library can check the version by call- + ing pcre2_config() with appropriate arguments. Users of applications + that do not have access to the underlying code cannot do this. A spe- + cial "condition" called VERSION exists to allow such users to discover which version of PCRE2 they are dealing with by using this condition to - match a string such as "yesno". VERSION must be followed either by "=" + match a string such as "yesno". VERSION must be followed either by "=" or ">=" and a version number. For example: (?(VERSION>=10.4)yes|no) - This pattern matches "yes" if the PCRE2 version is greater or equal to - 10.4, or "no" otherwise. The fractional part of the version number may + This pattern matches "yes" if the PCRE2 version is greater or equal to + 10.4, or "no" otherwise. The fractional part of the version number may not contain more than two digits. Assertion conditions - If the condition is not in any of the above formats, it must be a - parenthesized assertion. This may be a positive or negative lookahead - or lookbehind assertion. Consider this pattern, again containing non- - significant white space, and with the two alternatives on the second - line: + If the condition is not in any of the above formats, it must be an + assertion. This may be a positive or negative lookahead or lookbehind + assertion. Consider this pattern, again containing non-significant + white space, and with the two alternatives on the second line: (?(?=[^a-z]*[a-z]) \d{2}-[a-z]{3}-\d{2} | \d{2}-\d{2}-\d{2} ) @@ -8556,12 +8280,12 @@ CONDITIONAL GROUPS strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are letters and dd are digits. - When an assertion that is a condition contains capture groups, any cap- - turing that occurs in a matching branch is retained afterwards, for - both positive and negative assertions, because matching always contin- - ues after the assertion, whether it succeeds or fails. (Compare non- - conditional assertions, for which captures are retained only for posi- - tive assertions that succeed.) + When an assertion that is a condition contains capturing subpatterns, + any capturing that occurs in a matching branch is retained afterwards, + for both positive and negative assertions, because matching always con- + tinues after the assertion, whether it succeeds or fails. (Compare non- + conditional assertions, when captures are retained only for positive + assertions that succeed.) COMMENTS @@ -8569,8 +8293,8 @@ COMMENTS There are two ways of including comments in patterns that are processed by PCRE2. In both cases, the start of the comment must not be in a character class, nor in the middle of any other sequence of related - characters such as (?: or a group name or number. The characters that - make up a comment play no part in the pattern matching. + characters such as (?: or a subpattern name or number. The characters + that make up a comment play no part in the pattern matching. The sequence (?# marks the start of a comment that continues up to the next closing parenthesis. Nested parentheses are not permitted. If the @@ -8615,14 +8339,14 @@ RECURSIVE PATTERNS Obviously, PCRE2 cannot support the interpolation of Perl code. Instead, it supports special syntax for recursion of the entire pat- - tern, and also for individual capture group recursion. After its intro- - duction in PCRE1 and Python, this kind of recursion was subsequently + tern, and also for individual subpattern recursion. After its introduc- + tion in PCRE1 and Python, this kind of recursion was subsequently introduced into Perl at release 5.10. A special item that consists of (? followed by a number greater than zero and a closing parenthesis is a recursive subroutine call of the - capture group of the given number, provided that it occurs inside that - group. (If not, it is a non-recursive subroutine call, which is + subpattern of the given number, provided that it occurs inside that + subpattern. (If not, it is a non-recursive subroutine call, which is described in the next section.) The special item (?R) or (?0) is a recursive call of the entire regular expression. @@ -8653,136 +8377,137 @@ RECURSIVE PATTERNS words, a negative number counts capturing parentheses leftwards from the point at which it is encountered. - Be aware however, that if duplicate capture group numbers are in use, - relative references refer to the earliest group with the appropriate + Be aware however, that if duplicate subpattern numbers are in use, rel- + ative references refer to the earliest subpattern with the appropriate number. Consider, for example: (?|(a)|(b)) (c) (?-2) - The first two capture groups (a) and (b) are both numbered 1, and group - (c) is number 2. When the reference (?-2) is encountered, the second - most recently opened parentheses has the number 1, but it is the first - such group (the (a) group) to which the recursion refers. This would be - the same if an absolute reference (?1) was used. In other words, rela- - tive references are just a shorthand for computing a group number. - - It is also possible to refer to subsequent capture groups, by writing - references such as (?+2). However, these cannot be recursive because - the reference is not inside the parentheses that are referenced. They - are always non-recursive subroutine calls, as described in the next - section. - - An alternative approach is to use named parentheses. The Perl syntax - for this is (?&name); PCRE1's earlier syntax (?P>name) is also sup- + The first two capturing groups (a) and (b) are both numbered 1, and + group (c) is number 2. When the reference (?-2) is encountered, the + second most recently opened parentheses has the number 1, but it is the + first such group (the (a) group) to which the recursion refers. This + would be the same if an absolute reference (?1) was used. In other + words, relative references are just a shorthand for computing a group + number. + + It is also possible to refer to subsequently opened parentheses, by + writing references such as (?+2). However, these cannot be recursive + because the reference is not inside the parentheses that are refer- + enced. They are always non-recursive subroutine calls, as described in + the next section. + + An alternative approach is to use named parentheses. The Perl syntax + for this is (?&name); PCRE1's earlier syntax (?P>name) is also sup- ported. We could rewrite the above example as follows: (?<pn> \( ( [^()]++ | (?&pn) )* \) ) - If there is more than one group with the same name, the earliest one is - used. + If there is more than one subpattern with the same name, the earliest + one is used. The example pattern that we have been looking at contains nested unlim- - ited repeats, and so the use of a possessive quantifier for matching - strings of non-parentheses is important when applying the pattern to + ited repeats, and so the use of a possessive quantifier for matching + strings of non-parentheses is important when applying the pattern to strings that do not match. For example, when this pattern is applied to (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa() - it yields "no match" quickly. However, if a possessive quantifier is - not used, the match runs for a very long time indeed because there are - so many different ways the + and * repeats can carve up the subject, + it yields "no match" quickly. However, if a possessive quantifier is + not used, the match runs for a very long time indeed because there are + so many different ways the + and * repeats can carve up the subject, and all have to be tested before failure can be reported. - At the end of a match, the values of capturing parentheses are those - from the outermost level. If you want to obtain intermediate values, a + At the end of a match, the values of capturing parentheses are those + from the outermost level. If you want to obtain intermediate values, a callout function can be used (see below and the pcre2callout documenta- tion). If the pattern above is matched against (ab(cd)ef) - the value for the inner capturing parentheses (numbered 2) is "ef", - which is the last value taken on at the top level. If a capture group - is not matched at the top level, its final captured value is unset, - even if it was (temporarily) set at a deeper level during the matching - process. + the value for the inner capturing parentheses (numbered 2) is "ef", + which is the last value taken on at the top level. If a capturing sub- + pattern is not matched at the top level, its final captured value is + unset, even if it was (temporarily) set at a deeper level during the + matching process. - Do not confuse the (?R) item with the condition (R), which tests for - recursion. Consider this pattern, which matches text in angle brack- - ets, allowing for arbitrary nesting. Only digits are allowed in nested - brackets (that is, when recursing), whereas any characters are permit- + Do not confuse the (?R) item with the condition (R), which tests for + recursion. Consider this pattern, which matches text in angle brack- + ets, allowing for arbitrary nesting. Only digits are allowed in nested + brackets (that is, when recursing), whereas any characters are permit- ted at the outer level. < (?: (?(R) \d++ | [^<>]*+) | (?R)) * > - In this pattern, (?(R) is the start of a conditional group, with two - different alternatives for the recursive and non-recursive cases. The - (?R) item is the actual recursive call. + In this pattern, (?(R) is the start of a conditional subpattern, with + two different alternatives for the recursive and non-recursive cases. + The (?R) item is the actual recursive call. Differences in recursion processing between PCRE2 and Perl Some former differences between PCRE2 and Perl no longer exist. - Before release 10.30, recursion processing in PCRE2 differed from Perl - in that a recursive subroutine call was always treated as an atomic - group. That is, once it had matched some of the subject string, it was - never re-entered, even if it contained untried alternatives and there - was a subsequent matching failure. (Historical note: PCRE implemented + Before release 10.30, recursion processing in PCRE2 differed from Perl + in that a recursive subpattern call was always treated as an atomic + group. That is, once it had matched some of the subject string, it was + never re-entered, even if it contained untried alternatives and there + was a subsequent matching failure. (Historical note: PCRE implemented recursion before Perl did.) - Starting with release 10.30, recursive subroutine calls are no longer + Starting with release 10.30, recursive subroutine calls are no longer treated as atomic. That is, they can be re-entered to try unused alter- - natives if there is a matching failure later in the pattern. This is - now compatible with the way Perl works. If you want a subroutine call + natives if there is a matching failure later in the pattern. This is + now compatible with the way Perl works. If you want a subroutine call to be atomic, you must explicitly enclose it in an atomic group. - Supporting backtracking into recursions simplifies certain types of + Supporting backtracking into recursions simplifies certain types of recursive pattern. For example, this pattern matches palindromic strings: ^((.)(?1)\2|.?)$ - The second branch in the group matches a single central character in - the palindrome when there are an odd number of characters, or nothing - when there are an even number of characters, but in order to work it - has to be able to try the second case when the rest of the pattern + The second branch in the group matches a single central character in + the palindrome when there are an odd number of characters, or nothing + when there are an even number of characters, but in order to work it + has to be able to try the second case when the rest of the pattern match fails. If you want to match typical palindromic phrases, the pat- - tern has to ignore all non-word characters, which can be done like + tern has to ignore all non-word characters, which can be done like this: ^\W*+((.)\W*+(?1)\W*+\2|\W*+.?)\W*+$ - If run with the PCRE2_CASELESS option, this pattern matches phrases - such as "A man, a plan, a canal: Panama!". Note the use of the posses- - sive quantifier *+ to avoid backtracking into sequences of non-word + If run with the PCRE2_CASELESS option, this pattern matches phrases + such as "A man, a plan, a canal: Panama!". Note the use of the posses- + sive quantifier *+ to avoid backtracking into sequences of non-word characters. Without this, PCRE2 takes a great deal longer (ten times or - more) to match typical phrases, and Perl takes so long that you think + more) to match typical phrases, and Perl takes so long that you think it has gone into a loop. - Another way in which PCRE2 and Perl used to differ in their recursion - processing is in the handling of captured values. Formerly in Perl, - when a group was called recursively or as a subroutine (see the next - section), it had no access to any values that were captured outside the - recursion, whereas in PCRE2 these values can be referenced. Consider - this pattern: + Another way in which PCRE2 and Perl used to differ in their recursion + processing is in the handling of captured values. Formerly in Perl, + when a subpattern was called recursively or as a subpattern (see the + next section), it had no access to any values that were captured out- + side the recursion, whereas in PCRE2 these values can be referenced. + Consider this pattern: ^(.)(\1|a(?2)) - This pattern matches "bab". The first capturing parentheses match "b", + This pattern matches "bab". The first capturing parentheses match "b", then in the second group, when the backreference \1 fails to match "b", the second alternative matches "a" and then recurses. In the recursion, - \1 does now match "b" and so the whole match succeeds. This match used + \1 does now match "b" and so the whole match succeeds. This match used to fail in Perl, but in later versions (I tried 5.024) it now works. -GROUPS AS SUBROUTINES +SUBPATTERNS AS SUBROUTINES - If the syntax for a recursive group call (either by number or by name) - is used outside the parentheses to which it refers, it operates a bit - like a subroutine in a programming language. More accurately, PCRE2 - treats the referenced group as an independent subpattern which it tries - to match at the current matching position. The called group may be - defined before or after the reference. A numbered reference can be - absolute or relative, as in these examples: + If the syntax for a recursive subpattern call (either by number or by + name) is used outside the parentheses to which it refers, it operates a + bit like a subroutine in a programming language. More accurately, PCRE2 + treats the referenced subpattern as an independent subpattern which it + tries to match at the current matching position. The called subpattern + may be defined before or after the reference. A numbered reference can + be absolute or relative, as in these examples: (...(absolute)...)...(?2)... (...(relative)...)...(?-1)... @@ -8792,106 +8517,106 @@ GROUPS AS SUBROUTINES (sens|respons)e and \1ibility - matches "sense and sensibility" and "response and responsibility", but + matches "sense and sensibility" and "response and responsibility", but not "sense and responsibility". If instead the pattern (sens|respons)e and (?1)ibility - is used, it does match "sense and responsibility" as well as the other - two strings. Another example is given in the discussion of DEFINE + is used, it does match "sense and responsibility" as well as the other + two strings. Another example is given in the discussion of DEFINE above. - Like recursions, subroutine calls used to be treated as atomic, but - this changed at PCRE2 release 10.30, so backtracking into subroutine - calls can now occur. However, any capturing parentheses that are set + Like recursions, subroutine calls used to be treated as atomic, but + this changed at PCRE2 release 10.30, so backtracking into subroutine + calls can now occur. However, any capturing parentheses that are set during the subroutine call revert to their previous values afterwards. - Processing options such as case-independence are fixed when a group is - defined, so if it is used as a subroutine, such options cannot be - changed for different calls. For example, consider this pattern: + Processing options such as case-independence are fixed when a subpat- + tern is defined, so if it is used as a subroutine, such options cannot + be changed for different calls. For example, consider this pattern: (abc)(?i:(?-1)) - It matches "abcabc". It does not match "abcABC" because the change of - processing option does not affect the called group. + It matches "abcabc". It does not match "abcABC" because the change of + processing option does not affect the called subpattern. - The behaviour of backtracking control verbs in groups when called as - subroutines is described in the section entitled "Backtracking verbs in - subroutines" below. + The behaviour of backtracking control verbs in subpatterns when called + as subroutines is described in the section entitled "Backtracking verbs + in subroutines" below. ONIGURUMA SUBROUTINE SYNTAX - For compatibility with Oniguruma, the non-Perl syntax \g followed by a + For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or a number enclosed either in angle brackets or single quotes, is - an alternative syntax for calling a group as a subroutine, possibly - recursively. Here are two of the examples used above, rewritten using - this syntax: + an alternative syntax for referencing a subpattern as a subroutine, + possibly recursively. Here are two of the examples used above, rewrit- + ten using this syntax: (?<pn> \( ( (?>[^()]+) | \g<pn> )* \) ) (sens|respons)e and \g'1'ibility - PCRE2 supports an extension to Oniguruma: if a number is preceded by a + PCRE2 supports an extension to Oniguruma: if a number is preceded by a plus or a minus sign it is taken as a relative reference. For example: (abc)(?i:\g<-1>) - Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not - synonymous. The former is a backreference; the latter is a subroutine + Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not + synonymous. The former is a backreference; the latter is a subroutine call. CALLOUTS Perl has a feature whereby using the sequence (?{...}) causes arbitrary - Perl code to be obeyed in the middle of matching a regular expression. + Perl code to be obeyed in the middle of matching a regular expression. This makes it possible, amongst other things, to extract different sub- strings that match the same pair of parentheses when there is a repeti- tion. - PCRE2 provides a similar feature, but of course it cannot obey arbi- - trary Perl code. The feature is called "callout". The caller of PCRE2 - provides an external function by putting its entry point in a match - context using the function pcre2_set_callout(), and then passing that - context to pcre2_match() or pcre2_dfa_match(). If no match context is + PCRE2 provides a similar feature, but of course it cannot obey arbi- + trary Perl code. The feature is called "callout". The caller of PCRE2 + provides an external function by putting its entry point in a match + context using the function pcre2_set_callout(), and then passing that + context to pcre2_match() or pcre2_dfa_match(). If no match context is passed, or if the callout entry point is set to NULL, callouts are dis- abled. - Within a regular expression, (?C<arg>) indicates a point at which the - external function is to be called. There are two kinds of callout: - those with a numerical argument and those with a string argument. (?C) - on its own with no argument is treated as (?C0). A numerical argument - allows the application to distinguish between different callouts. - String arguments were added for release 10.20 to make it possible for - script languages that use PCRE2 to embed short scripts within patterns + Within a regular expression, (?C<arg>) indicates a point at which the + external function is to be called. There are two kinds of callout: + those with a numerical argument and those with a string argument. (?C) + on its own with no argument is treated as (?C0). A numerical argument + allows the application to distinguish between different callouts. + String arguments were added for release 10.20 to make it possible for + script languages that use PCRE2 to embed short scripts within patterns in a similar way to Perl. During matching, when PCRE2 reaches a callout point, the external func- - tion is called. It is provided with the number or string argument of - the callout, the position in the pattern, and one item of data that is + tion is called. It is provided with the number or string argument of + the callout, the position in the pattern, and one item of data that is also set in the match block. The callout function may cause matching to proceed, to backtrack, or to fail. - By default, PCRE2 implements a number of optimizations at matching - time, and one side-effect is that sometimes callouts are skipped. If - you need all possible callouts to happen, you need to set options that - disable the relevant optimizations. More details, including a complete - description of the programming interface to the callout function, are + By default, PCRE2 implements a number of optimizations at matching + time, and one side-effect is that sometimes callouts are skipped. If + you need all possible callouts to happen, you need to set options that + disable the relevant optimizations. More details, including a complete + description of the programming interface to the callout function, are given in the pcre2callout documentation. Callouts with numerical arguments - If you just want to have a means of identifying different callout - points, put a number less than 256 after the letter C. For example, + If you just want to have a means of identifying different callout + points, put a number less than 256 after the letter C. For example, this pattern has two callout points: (?C1)abc(?C2)def - If the PCRE2_AUTO_CALLOUT flag is passed to pcre2_compile(), numerical - callouts are automatically installed before each item in the pattern. - They are all numbered 255. If there is a conditional group in the pat- + If the PCRE2_AUTO_CALLOUT flag is passed to pcre2_compile(), numerical + callouts are automatically installed before each item in the pattern. + They are all numbered 255. If there is a conditional group in the pat- tern whose condition is an assertion, an additional callout is inserted - just before the condition. An explicit callout may also be set at this + just before the condition. An explicit callout may also be set at this position, as in this example: (?(?C9)(?=a)abc|def) @@ -8901,26 +8626,25 @@ CALLOUTS Callouts with string arguments - A delimited string may be used instead of a number as a callout argu- - ment. The starting delimiter must be one of ` ' " ^ % # $ { and the + A delimited string may be used instead of a number as a callout argu- + ment. The starting delimiter must be one of ` ' " ^ % # $ { and the ending delimiter is the same as the start, except for {, where the end- - ing delimiter is }. If the ending delimiter is needed within the + ing delimiter is }. If the ending delimiter is needed within the string, it must be doubled. For example: (?C'ab ''c'' d')xyz(?C{any text})pqr - The doubling is removed before the string is passed to the callout + The doubling is removed before the string is passed to the callout function. BACKTRACKING CONTROL - There are a number of special "Backtracking Control Verbs" (to use - Perl's terminology) that modify the behaviour of backtracking during - matching. They are generally of the form (*VERB) or (*VERB:NAME). Some - verbs take either form, possibly behaving differently depending on - whether or not a name is present. The names are not required to be - unique within the pattern. + There are a number of special "Backtracking Control Verbs" (to use + Perl's terminology) that modify the behaviour of backtracking during + matching. They are generally of the form (*VERB) or (*VERB:NAME). Some + verbs take either form, possibly behaving differently depending on + whether or not a name is present. By default, for compatibility with Perl, a name is any sequence of characters that does not include a closing parenthesis. The name is not @@ -8956,8 +8680,8 @@ BACKTRACKING CONTROL by the DFA matching function. The behaviour of these verbs in repeated groups, assertions, and in - capture groups called as subroutines (whether or not recursively) is - documented below. + subpatterns called as subroutines (whether or not recursively) is docu- + mented below. Optimizations that affect backtracking verbs @@ -8982,8 +8706,8 @@ BACKTRACKING CONTROL (*ACCEPT) or (*ACCEPT:NAME) This verb causes the match to end successfully, skipping the remainder - of the pattern. However, when it is inside a capture group that is - called as a subroutine, only that group is ended successfully. Matching + of the pattern. However, when it is inside a subpattern that is called + as a subroutine, only that subpattern is ended successfully. Matching then continues at the outer level. If (*ACCEPT) in triggered in a posi- tive assertion, the assertion succeeds; in a negative assertion, the assertion fails. @@ -8996,10 +8720,6 @@ BACKTRACKING CONTROL This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- tured by the outer parentheses. - Warning: (*ACCEPT) should not be used within a script run group, - because it causes an immediate exit from the group, bypassing the - script run checking. - (*FAIL) or (*FAIL:NAME) This verb causes a matching failure, forcing backtracking to occur. It @@ -9014,8 +8734,8 @@ BACKTRACKING CONTROL A match with the string "aaaa" always fails, but the callout is taken before each backtrack happens (in this example, 10 times). - (*ACCEPT:NAME) and (*FAIL:NAME) are treated as (*MARK:NAME)(*ACCEPT) - and (*MARK:NAME)(*FAIL), respectively. + (*ACCEPT:NAME) and (*FAIL:NAME) behave exactly the same as + (*MARK:NAME)(*ACCEPT) and (*MARK:NAME)(*FAIL), respectively. Recording which path was taken @@ -9025,21 +8745,24 @@ BACKTRACKING CONTROL (*MARK:NAME) or (*:NAME) - A name is always required with this verb. For all the other backtrack- - ing control verbs, a NAME argument is optional. + A name is always required with this verb. There may be as many + instances of (*MARK) as you like in a pattern, and their names do not + have to be unique. - When a match succeeds, the name of the last-encountered mark name on + When a match succeeds, the name of the last-encountered (*MARK:NAME) on the matching path is passed back to the caller as described in the sec- tion entitled "Other information about the match" in the pcre2api docu- - mentation. This applies to all instances of (*MARK) and other verbs, - including those inside assertions and atomic groups. However, there are - differences in those cases when (*MARK) is used in conjunction with - (*SKIP) as described below. + mentation. This applies to all instances of (*MARK), including those + inside assertions and atomic groups. (There are differences in those + cases when (*MARK) is used in conjunction with (*SKIP) as described + below.) + + As well as (*MARK), the (*COMMIT), (*PRUNE) and (*THEN) verbs may have + associated NAME arguments. Whichever is last on the matching path is + passed back. See below for more details of these other verbs. - The mark name that was last encountered on the matching path is passed - back. A verb without a NAME argument is ignored for this purpose. Here - is an example of pcre2test output, where the "mark" modifier requests - the retrieval and outputting of (*MARK) data: + Here is an example of pcre2test output, where the "mark" modifier + requests the retrieval and outputting of (*MARK) data: re> /X(*MARK:A)Y|X(*MARK:B)Z/mark data> XY @@ -9050,76 +8773,76 @@ BACKTRACKING CONTROL MK: B The (*MARK) name is tagged with "MK:" in this output, and in this exam- - ple it indicates which of the two alternatives matched. This is a more - efficient way of obtaining this information than putting each alterna- + ple it indicates which of the two alternatives matched. This is a more + efficient way of obtaining this information than putting each alterna- tive in its own capturing parentheses. - If a verb with a name is encountered in a positive assertion that is - true, the name is recorded and passed back if it is the last-encoun- + If a verb with a name is encountered in a positive assertion that is + true, the name is recorded and passed back if it is the last-encoun- tered. This does not happen for negative assertions or failing positive assertions. - After a partial match or a failed match, the last encountered name in + After a partial match or a failed match, the last encountered name in the entire match process is returned. For example: re> /X(*MARK:A)Y|X(*MARK:B)Z/mark data> XP No match, mark = B - Note that in this unanchored example the mark is retained from the + Note that in this unanchored example the mark is retained from the match attempt that started at the letter "X" in the subject. Subsequent match attempts starting at "P" and then with an empty string do not get as far as the (*MARK) item, but nevertheless do not reset it. - If you are interested in (*MARK) values after failed matches, you - should probably set the PCRE2_NO_START_OPTIMIZE option (see above) to + If you are interested in (*MARK) values after failed matches, you + should probably set the PCRE2_NO_START_OPTIMIZE option (see above) to ensure that the match is always attempted. Verbs that act after backtracking The following verbs do nothing when they are encountered. Matching con- - tinues with what follows, but if there is a subsequent match failure, - causing a backtrack to the verb, a failure is forced. That is, back- - tracking cannot pass to the left of the verb. However, when one of + tinues with what follows, but if there is a subsequent match failure, + causing a backtrack to the verb, a failure is forced. That is, back- + tracking cannot pass to the left of the verb. However, when one of these verbs appears inside an atomic group or in a lookaround assertion - that is true, its effect is confined to that group, because once the - group has been matched, there is never any backtracking into it. Back- + that is true, its effect is confined to that group, because once the + group has been matched, there is never any backtracking into it. Back- tracking from beyond an assertion or an atomic group ignores the entire - group, and seeks a preceding backtracking point. + group, and seeks a preceeding backtracking point. - These verbs differ in exactly what kind of failure occurs when back- - tracking reaches them. The behaviour described below is what happens - when the verb is not in a subroutine or an assertion. Subsequent sec- + These verbs differ in exactly what kind of failure occurs when back- + tracking reaches them. The behaviour described below is what happens + when the verb is not in a subroutine or an assertion. Subsequent sec- tions cover these special cases. (*COMMIT) or (*COMMIT:NAME) - This verb causes the whole match to fail outright if there is a later + This verb causes the whole match to fail outright if there is a later matching failure that causes backtracking to reach it. Even if the pat- - tern is unanchored, no further attempts to find a match by advancing - the starting point take place. If (*COMMIT) is the only backtracking + tern is unanchored, no further attempts to find a match by advancing + the starting point take place. If (*COMMIT) is the only backtracking verb that is encountered, once it has been passed pcre2_match() is com- mitted to finding a match at the current starting point, or not at all. For example: a+(*COMMIT)b - This matches "xxaab" but not "aacaab". It can be thought of as a kind + This matches "xxaab" but not "aacaab". It can be thought of as a kind of dynamic anchor, or "I've started, so I must finish." - The behaviour of (*COMMIT:NAME) is not the same as (*MARK:NAME)(*COM- - MIT). It is like (*MARK:NAME) in that the name is remembered for pass- - ing back to the caller. However, (*SKIP:NAME) searches only for names - that are set with (*MARK), ignoring those set by any of the other back- - tracking verbs. + The behaviour of (*COMMIT:NAME) is not the same as (*MARK:NAME)(*COM- + MIT). It is like (*MARK:NAME) in that the name is remembered for pass- + ing back to the caller. However, (*SKIP:NAME) searches only for names + set with (*MARK), ignoring those set by (*COMMIT), (*PRUNE) and + (*THEN). - If there is more than one backtracking verb in a pattern, a different - one that follows (*COMMIT) may be triggered first, so merely passing + If there is more than one backtracking verb in a pattern, a different + one that follows (*COMMIT) may be triggered first, so merely passing (*COMMIT) during a match does not always guarantee that a match must be at this starting point. - Note that (*COMMIT) at the start of a pattern is not the same as an - anchor, unless PCRE2's start-of-match optimizations are turned off, as + Note that (*COMMIT) at the start of a pattern is not the same as an + anchor, unless PCRE2's start-of-match optimizations are turned off, as shown in this output from pcre2test: re> /(*COMMIT)abc/ @@ -9130,63 +8853,63 @@ BACKTRACKING CONTROL data> xyzabc No match - For the first pattern, PCRE2 knows that any match must start with "a", - so the optimization skips along the subject to "a" before applying the - pattern to the first set of data. The match attempt then succeeds. The - second pattern disables the optimization that skips along to the first - character. The pattern is now applied starting at "x", and so the - (*COMMIT) causes the match to fail without trying any other starting + For the first pattern, PCRE2 knows that any match must start with "a", + so the optimization skips along the subject to "a" before applying the + pattern to the first set of data. The match attempt then succeeds. The + second pattern disables the optimization that skips along to the first + character. The pattern is now applied starting at "x", and so the + (*COMMIT) causes the match to fail without trying any other starting points. (*PRUNE) or (*PRUNE:NAME) - This verb causes the match to fail at the current starting position in + This verb causes the match to fail at the current starting position in the subject if there is a later matching failure that causes backtrack- - ing to reach it. If the pattern is unanchored, the normal "bumpalong" - advance to the next starting character then happens. Backtracking can - occur as usual to the left of (*PRUNE), before it is reached, or when - matching to the right of (*PRUNE), but if there is no match to the - right, backtracking cannot cross (*PRUNE). In simple cases, the use of - (*PRUNE) is just an alternative to an atomic group or possessive quan- + ing to reach it. If the pattern is unanchored, the normal "bumpalong" + advance to the next starting character then happens. Backtracking can + occur as usual to the left of (*PRUNE), before it is reached, or when + matching to the right of (*PRUNE), but if there is no match to the + right, backtracking cannot cross (*PRUNE). In simple cases, the use of + (*PRUNE) is just an alternative to an atomic group or possessive quan- tifier, but there are some uses of (*PRUNE) that cannot be expressed in - any other way. In an anchored pattern (*PRUNE) has the same effect as + any other way. In an anchored pattern (*PRUNE) has the same effect as (*COMMIT). The behaviour of (*PRUNE:NAME) is not the same as (*MARK:NAME)(*PRUNE). It is like (*MARK:NAME) in that the name is remembered for passing back - to the caller. However, (*SKIP:NAME) searches only for names set with - (*MARK), ignoring those set by other backtracking verbs. + to the caller. However, (*SKIP:NAME) searches only for names set with + (*MARK), ignoring those set by (*COMMIT), (*PRUNE) or (*THEN). (*SKIP) - This verb, when given without a name, is like (*PRUNE), except that if - the pattern is unanchored, the "bumpalong" advance is not to the next + This verb, when given without a name, is like (*PRUNE), except that if + the pattern is unanchored, the "bumpalong" advance is not to the next character, but to the position in the subject where (*SKIP) was encoun- - tered. (*SKIP) signifies that whatever text was matched leading up to - it cannot be part of a successful match if there is a later mismatch. + tered. (*SKIP) signifies that whatever text was matched leading up to + it cannot be part of a successful match if there is a later mismatch. Consider: a+(*SKIP)b - If the subject is "aaaac...", after the first match attempt fails - (starting at the first character in the string), the starting point + If the subject is "aaaac...", after the first match attempt fails + (starting at the first character in the string), the starting point skips on to start the next attempt at "c". Note that a possessive quan- - tifer does not have the same effect as this example; although it would - suppress backtracking during the first match attempt, the second - attempt would start at the second character instead of skipping on to + tifer does not have the same effect as this example; although it would + suppress backtracking during the first match attempt, the second + attempt would start at the second character instead of skipping on to "c". (*SKIP:NAME) - When (*SKIP) has an associated name, its behaviour is modified. When - such a (*SKIP) is triggered, the previous path through the pattern is - searched for the most recent (*MARK) that has the same name. If one is - found, the "bumpalong" advance is to the subject position that corre- - sponds to that (*MARK) instead of to where (*SKIP) was encountered. If + When (*SKIP) has an associated name, its behaviour is modified. When + such a (*SKIP) is triggered, the previous path through the pattern is + searched for the most recent (*MARK) that has the same name. If one is + found, the "bumpalong" advance is to the subject position that corre- + sponds to that (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a matching name is found, the (*SKIP) is ignored. - The search for a (*MARK) name uses the normal backtracking mechanism, - which means that it does not see (*MARK) settings that are inside + The search for a (*MARK) name uses the normal backtracking mechanism, + which means that it does not see (*MARK) settings that are inside atomic groups or assertions, because they are never re-entered by back- tracking. Compare the following pcre2test examples: @@ -9200,18 +8923,19 @@ BACKTRACKING CONTROL 0: b 1: b - In the first example, the (*MARK) setting is in an atomic group, so it + In the first example, the (*MARK) setting is in an atomic group, so it is not seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored. - This allows the second branch of the pattern to be tried at the first - character position. In the second example, the (*MARK) setting is not - in an atomic group. This allows (*SKIP:X) to find the (*MARK) when it + This allows the second branch of the pattern to be tried at the first + character position. In the second example, the (*MARK) setting is not + in an atomic group. This allows (*SKIP:X) to find the (*MARK) when it backtracks, and this causes a new matching attempt to start at the sec- - ond character. This time, the (*MARK) is never seen because "a" does + ond character. This time, the (*MARK) is never seen because "a" does not match "b", so the matcher immediately jumps to the second branch of the pattern. - Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It - ignores names that are set by other backtracking verbs. + Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It + ignores names that are set by (*COMMIT:NAME), (*PRUNE:NAME) or + (*THEN:NAME). (*THEN) or (*THEN:NAME) @@ -9233,12 +8957,12 @@ BACKTRACKING CONTROL The behaviour of (*THEN:NAME) is not the same as (*MARK:NAME)(*THEN). It is like (*MARK:NAME) in that the name is remembered for passing back to the caller. However, (*SKIP:NAME) searches only for names set with - (*MARK), ignoring those set by other backtracking verbs. + (*MARK), ignoring those set by (*COMMIT), (*PRUNE) and (*THEN). - A group that does not contain a | character is just a part of the + A subpattern that does not contain a | character is just a part of the enclosing alternative; it is not a nested alternation with only one - alternative. The effect of (*THEN) extends beyond such a group to the - enclosing alternative. Consider this pattern, where A, B, etc. are + alternative. The effect of (*THEN) extends beyond such a subpattern to + the enclosing alternative. Consider this pattern, where A, B, etc. are complex pattern fragments that do not contain any | characters at this level: @@ -9246,20 +8970,20 @@ BACKTRACKING CONTROL If A and B are matched, but there is a failure in C, matching does not backtrack into A; instead it moves to the next alternative, that is, D. - However, if the group containing (*THEN) is given an alternative, it - behaves differently: + However, if the subpattern containing (*THEN) is given an alternative, + it behaves differently: A (B(*THEN)C | (*FAIL)) | D - The effect of (*THEN) is now confined to the inner group. After a fail- - ure in C, matching moves to (*FAIL), which causes the whole group to - fail because there are no more alternatives to try. In this case, - matching does backtrack into A. + The effect of (*THEN) is now confined to the inner subpattern. After a + failure in C, matching moves to (*FAIL), which causes the whole subpat- + tern to fail because there are no more alternatives to try. In this + case, matching does now backtrack into A. - Note that a conditional group is not considered as having two alterna- - tives, because only one is ever used. In other words, the | character - in a conditional group has a different meaning. Ignoring white space, - consider: + Note that a conditional subpattern is not considered as having two + alternatives, because only one is ever used. In other words, the | + character in a conditional subpattern has a different meaning. Ignoring + white space, consider: ^.*? (?(?=a) a | b(*THEN)c ) @@ -9267,10 +8991,10 @@ BACKTRACKING CONTROL ungreedy, it initially matches zero characters. The condition (?=a) then fails, the character "b" is matched, but "c" is not. At this point, matching does not backtrack to .*? as might perhaps be expected - from the presence of the | character. The conditional group is part of - the single alternative that comprises the whole pattern, and so the - match fails. (If there was a backtrack into .*?, allowing it to match - "b", the match would succeed.) + from the presence of the | character. The conditional subpattern is + part of the single alternative that comprises the whole pattern, and so + the match fails. (If there was a backtrack into .*?, allowing it to + match "b", the match would succeed.) The verbs just described provide four different "strengths" of control when subsequent matching fails. (*THEN) is the weakest, carrying on the @@ -9317,13 +9041,13 @@ BACKTRACKING CONTROL (*FAIL) in any assertion has its normal effect: it forces an immediate backtrack. The behaviour of the other backtracking verbs depends on whether or not the assertion is standalone or acting as the condition - in a conditional group. + in a conditional subpattern. (*ACCEPT) in a standalone positive assertion causes the assertion to - succeed without any further processing; captured strings and a mark + succeed without any further processing; captured strings and a (*MARK) name (if set) are retained. In a standalone negative assertion, (*ACCEPT) causes the assertion to fail without any further processing; - captured substrings and any mark name are discarded. + captured substrings and any (*MARK) name are discarded. If the assertion is a condition, (*ACCEPT) causes the condition to be true for a positive assertion and false for a negative one; captured @@ -9350,24 +9074,26 @@ BACKTRACKING CONTROL Backtracking verbs in subroutines - These behaviours occur whether or not the group is called recursively. + These behaviours occur whether or not the subpattern is called recur- + sively. - (*ACCEPT) in a group called as a subroutine causes the subroutine match - to succeed without any further processing. Matching then continues - after the subroutine call. Perl documents this behaviour. Perl's treat- - ment of the other verbs in subroutines is different in some cases. + (*ACCEPT) in a subpattern called as a subroutine causes the subroutine + match to succeed without any further processing. Matching then contin- + ues after the subroutine call. Perl documents this behaviour. Perl's + treatment of the other verbs in subroutines is different in some cases. - (*FAIL) in a group called as a subroutine has its normal effect: it - forces an immediate backtrack. + (*FAIL) in a subpattern called as a subroutine has its normal effect: + it forces an immediate backtrack. - (*COMMIT), (*SKIP), and (*PRUNE) cause the subroutine match to fail - when triggered by being backtracked to in a group called as a subrou- - tine. There is then a backtrack at the outer level. + (*COMMIT), (*SKIP), and (*PRUNE) cause the subroutine match to fail + when triggered by being backtracked to in a subpattern called as a sub- + routine. There is then a backtrack at the outer level. (*THEN), when triggered, skips to the next alternative in the innermost - enclosing group that has alternatives (its normal behaviour). However, - if there is no such group within the subroutine's group, the subroutine - match fails and there is a backtrack at the outer level. + enclosing group within the subpattern that has alternatives (its normal + behaviour). However, if there is no such group within the subroutine + subpattern, the subroutine match fails and there is a backtrack at the + outer level. SEE ALSO @@ -9385,8 +9111,8 @@ AUTHOR REVISION - Last updated: 12 February 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 04 September 2018 + Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ @@ -9410,9 +9136,9 @@ COMPILED PATTERN MEMORY USAGE code, so that most simple patterns do not use much memory for storing the compiled version. However, there is one case where the memory usage of a compiled pattern can be unexpectedly large. If a parenthesized - group has a quantifier with a minimum greater than 1 and/or a limited - maximum, the whole group is repeated in the compiled code. For example, - the pattern + subpattern has a quantifier with a minimum greater than 1 and/or a lim- + ited maximum, the whole subpattern is repeated in the compiled code. + For example, the pattern (abc|def){2,4} @@ -9620,8 +9346,8 @@ AUTHOR REVISION - Last updated: 03 February 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 25 April 2018 + Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ @@ -9636,56 +9362,33 @@ SYNOPSIS #include <pcre2posix.h> - int pcre2_regcomp(regex_t *preg, const char *pattern, + int regcomp(regex_t *preg, const char *pattern, int cflags); - int pcre2_regexec(const regex_t *preg, const char *string, + int regexec(const regex_t *preg, const char *string, size_t nmatch, regmatch_t pmatch[], int eflags); - size_t pcre2_regerror(int errcode, const regex_t *preg, + size_t regerror(int errcode, const regex_t *preg, char *errbuf, size_t errbuf_size); - void pcre2_regfree(regex_t *preg); + void regfree(regex_t *preg); DESCRIPTION This set of functions provides a POSIX-style API for the PCRE2 regular - expression 8-bit library. There are no POSIX-style wrappers for PCRE2's - 16-bit and 32-bit libraries. See the pcre2api documentation for a - description of PCRE2's native API, which contains much additional func- - tionality. - - The functions described here are wrapper functions that ultimately call - the PCRE2 native API. Their prototypes are defined in the pcre2posix.h - header file, and they all have unique names starting with pcre2_. How- - ever, the pcre2posix.h header also contains macro definitions that con- - vert the standard POSIX names such regcomp() into pcre2_regcomp() etc. - This means that a program can use the usual POSIX names without running - the risk of accidentally linking with POSIX functions from a different - library. - - On Unix-like systems the PCRE2 POSIX library is called libpcre2-posix, - so can be accessed by adding -lpcre2-posix to the command for linking - an application. Because the POSIX functions call the native ones, it is - also necessary to add -lpcre2-8. - - Although they are not defined as protypes in pcre2posix.h, the library - does contain functions with the POSIX names regcomp() etc. These simply - pass their arguments to the PCRE2 functions. These functions are pro- - vided for backwards compatibility with earlier versions of PCRE2, so - that existing programs do not have to be recompiled. - - Calling the header file pcre2posix.h avoids any conflict with other - POSIX libraries. It can, of course, be renamed or aliased as regex.h, - which is the "correct" name, if there is no clash. It provides two - structure types, regex_t for compiled internal forms, and regmatch_t - for returning captured substrings. It also defines some constants whose - names start with "REG_"; these are used for setting options and identi- - fying error codes. - - -USING THE POSIX FUNCTIONS + expression 8-bit library. See the pcre2api documentation for a descrip- + tion of PCRE2's native API, which contains much additional functional- + ity. There are no POSIX-style wrappers for PCRE2's 16-bit and 32-bit + libraries. + + The functions described here are just wrapper functions that ultimately + call the PCRE2 native API. Their prototypes are defined in the + pcre2posix.h header file, and on Unix systems the library itself is + called libpcre2-posix.a, so can be accessed by adding -lpcre2-posix to + the command for linking an application that uses them. Because the + POSIX functions call the native ones, it is also necessary to add + -lpcre2-8. Those POSIX option bits that can reasonably be mapped to PCRE2 native options have been implemented. In addition, the option REG_EXTENDED is @@ -9707,19 +9410,23 @@ USING THE POSIX FUNCTIONS POSIX-compatible, and in multi-unit encoding domains it is probably even less compatible. - The descriptions below use the actual names of the functions, but, as - described above, the standard POSIX names (without the pcre2_ prefix) - may also be used. + The header for these functions is supplied as pcre2posix.h to avoid any + potential clash with other POSIX libraries. It can, of course, be + renamed or aliased as regex.h, which is the "correct" name. It provides + two structure types, regex_t for compiled internal forms, and reg- + match_t for returning captured substrings. It also defines some con- + stants whose names start with "REG_"; these are used for setting + options and identifying error codes. COMPILING A PATTERN - The function pcre2_regcomp() is called to compile a pattern into an - internal form. By default, the pattern is a C string terminated by a - binary zero (but see REG_PEND below). The preg argument is a pointer to - a regex_t structure that is used as a base for storing information - about the compiled regular expression. (It is also used for input when - REG_PEND is set.) + The function regcomp() is called to compile a pattern into an internal + form. By default, the pattern is a C string terminated by a binary zero + (but see REG_PEND below). The preg argument is a pointer to a regex_t + structure that is used as a base for storing information about the com- + piled regular expression. (It is also used for input when REG_PEND is + set.) The argument cflags is either zero, or contains one or more of the bits defined by the following macros: @@ -9753,23 +9460,21 @@ COMPILING A PATTERN REG_NOSUB - When a pattern that is compiled with this flag is passed to - pcre2_regexec() for matching, the nmatch and pmatch arguments are - ignored, and no captured strings are returned. Versions of the PCRE - library prior to 10.22 used to set the PCRE2_NO_AUTO_CAPTURE compile - option, but this no longer happens because it disables the use of back- - references. + When a pattern that is compiled with this flag is passed to regexec() + for matching, the nmatch and pmatch arguments are ignored, and no cap- + tured strings are returned. Versions of the PCRE library prior to 10.22 + used to set the PCRE2_NO_AUTO_CAPTURE compile option, but this no + longer happens because it disables the use of backreferences. REG_PEND - If this option is set, the reg_endp field in the preg structure (which + If this option is set, the reg_endp field in the preg structure (which has the type const char *) must be set to point to the character beyond - the end of the pattern before calling pcre2_regcomp(). The pattern - itself may now contain binary zeros, which are treated as data charac- - ters. Without REG_PEND, a binary zero terminates the pattern and the - re_endp field is ignored. This is a GNU extension to the POSIX standard - and should be used with caution in software intended to be portable to - other systems. + the end of the pattern before calling regcomp(). The pattern itself may + now contain binary zeros, which are treated as data characters. Without + REG_PEND, a binary zero terminates the pattern and the re_endp field is + ignored. This is a GNU extension to the POSIX standard and should be + used with caution in software intended to be portable to other systems. REG_UCP @@ -9799,24 +9504,23 @@ COMPILING A PATTERN It does not affect the way newlines are matched by the dot metacharac- ter (they are not) or by a negative class such as [^a] (they are). - The yield of pcre2_regcomp() is zero on success, and non-zero other- - wise. The preg structure is filled in on success, and one other member - of the structure (as well as re_endp) is public: re_nsub contains the - number of capturing subpatterns in the regular expression. Various - error codes are defined in the header file. + The yield of regcomp() is zero on success, and non-zero otherwise. The + preg structure is filled in on success, and one other member of the + structure (as well as re_endp) is public: re_nsub contains the number + of capturing subpatterns in the regular expression. Various error codes + are defined in the header file. - NOTE: If the yield of pcre2_regcomp() is non-zero, you must not attempt - to use the contents of the preg structure. If, for example, you pass it - to pcre2_regexec(), the result is undefined and your program is likely - to crash. + NOTE: If the yield of regcomp() is non-zero, you must not attempt to + use the contents of the preg structure. If, for example, you pass it to + regexec(), the result is undefined and your program is likely to crash. MATCHING NEWLINE CHARACTERS This area is not simple, because POSIX and Perl take different views of - things. It is not possible to get PCRE2 to obey POSIX semantics, but + things. It is not possible to get PCRE2 to obey POSIX semantics, but then PCRE2 was never intended to be a POSIX engine. The following table - lists the different possibilities for matching newline characters in + lists the different possibilities for matching newline characters in Perl and PCRE2: Default Change with @@ -9837,25 +9541,25 @@ MATCHING NEWLINE CHARACTERS $ matches \n in middle no REG_NEWLINE ^ matches \n in middle no REG_NEWLINE - This behaviour is not what happens when PCRE2 is called via its POSIX - API. By default, PCRE2's behaviour is the same as Perl's, except that - there is no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 + This behaviour is not what happens when PCRE2 is called via its POSIX + API. By default, PCRE2's behaviour is the same as Perl's, except that + there is no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, there is no way to stop newline from matching [^a]. - Default POSIX newline handling can be obtained by setting PCRE2_DOTALL - and PCRE2_DOLLAR_ENDONLY when calling pcre2_compile() directly, but - there is no way to make PCRE2 behave exactly as for the REG_NEWLINE - action. When using the POSIX API, passing REG_NEWLINE to PCRE2's - pcre2_regcomp() function causes PCRE2_MULTILINE to be passed to - pcre2_compile(), and REG_DOTALL passes PCRE2_DOTALL. There is no way to - pass PCRE2_DOLLAR_ENDONLY. + Default POSIX newline handling can be obtained by setting PCRE2_DOTALL + and PCRE2_DOLLAR_ENDONLY when calling pcre2_compile() directly, but + there is no way to make PCRE2 behave exactly as for the REG_NEWLINE + action. When using the POSIX API, passing REG_NEWLINE to PCRE2's reg- + comp() function causes PCRE2_MULTILINE to be passed to pcre2_compile(), + and REG_DOTALL passes PCRE2_DOTALL. There is no way to pass PCRE2_DOL- + LAR_ENDONLY. MATCHING A PATTERN - The function pcre2_regexec() is called to match a compiled pattern preg - against a given string, which is by default terminated by a zero byte - (but see REG_STARTEND below), subject to the options in eflags. These + The function regexec() is called to match a compiled pattern preg + against a given string, which is by default terminated by a zero byte + (but see REG_STARTEND below), subject to the options in eflags. These can be: REG_NOTBOL @@ -9865,9 +9569,9 @@ MATCHING A PATTERN REG_NOTEMPTY - The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 - matching function. Note that REG_NOTEMPTY is not part of the POSIX - standard. However, setting this option can give more POSIX-like behav- + The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 + matching function. Note that REG_NOTEMPTY is not part of the POSIX + standard. However, setting this option can give more POSIX-like behav- iour in some situations. REG_NOTEOL @@ -9877,30 +9581,29 @@ MATCHING A PATTERN REG_STARTEND - When this option is set, the subject string starts at string + - pmatch[0].rm_so and ends at string + pmatch[0].rm_eo, which should - point to the first character beyond the string. There may be binary - zeros within the subject string, and indeed, using REG_STARTEND is the + When this option is set, the subject string starts at string + + pmatch[0].rm_so and ends at string + pmatch[0].rm_eo, which should + point to the first character beyond the string. There may be binary + zeros within the subject string, and indeed, using REG_STARTEND is the only way to pass a subject string that contains a binary zero. - Whatever the value of pmatch[0].rm_so, the offsets of the matched - string and any captured substrings are still given relative to the - start of string itself. (Before PCRE2 release 10.30 these were given - relative to string + pmatch[0].rm_so, but this differs from other + Whatever the value of pmatch[0].rm_so, the offsets of the matched + string and any captured substrings are still given relative to the + start of string itself. (Before PCRE2 release 10.30 these were given + relative to string + pmatch[0].rm_so, but this differs from other implementations.) - This is a BSD extension, compatible with but not specified by IEEE - Standard 1003.2 (POSIX.2), and should be used with caution in software - intended to be portable to other systems. Note that a non-zero rm_so - does not imply REG_NOTBOL; REG_STARTEND affects only the location and - length of the string, not how it is matched. Setting REG_STARTEND and - passing pmatch as NULL are mutually exclusive; the error REG_INVARG is + This is a BSD extension, compatible with but not specified by IEEE + Standard 1003.2 (POSIX.2), and should be used with caution in software + intended to be portable to other systems. Note that a non-zero rm_so + does not imply REG_NOTBOL; REG_STARTEND affects only the location and + length of the string, not how it is matched. Setting REG_STARTEND and + passing pmatch as NULL are mutually exclusive; the error REG_INVARG is returned. - If the pattern was compiled with the REG_NOSUB flag, no data about any - matched strings is returned. The nmatch and pmatch arguments of - pcre2_regexec() are ignored (except possibly as input for REG_STAR- - TEND). + If the pattern was compiled with the REG_NOSUB flag, no data about any + matched strings is returned. The nmatch and pmatch arguments of + regexec() are ignored (except possibly as input for REG_STARTEND). The value of nmatch may be zero, and the value pmatch may be NULL (unless REG_STARTEND is set); in both these cases no data about any @@ -9923,22 +9626,22 @@ MATCHING A PATTERN ERROR MESSAGES - The pcre2_regerror() function maps a non-zero errorcode from either - pcre2_regcomp() or pcre2_regexec() to a printable message. If preg is - not NULL, the error should have arisen from the use of that structure. - A message terminated by a binary zero is placed in errbuf. If the buf- - fer is too short, only the first errbuf_size - 1 characters of the - error message are used. The yield of the function is the size of buffer - needed to hold the whole message, including the terminating zero. This - value is greater than errbuf_size if the message was truncated. + The regerror() function maps a non-zero errorcode from either regcomp() + or regexec() to a printable message. If preg is not NULL, the error + should have arisen from the use of that structure. A message terminated + by a binary zero is placed in errbuf. If the buffer is too short, only + the first errbuf_size - 1 characters of the error message are used. The + yield of the function is the size of buffer needed to hold the whole + message, including the terminating zero. This value is greater than + errbuf_size if the message was truncated. MEMORY USAGE Compiling a regular expression causes memory to be allocated and asso- - ciated with the preg structure. The function pcre2_regfree() frees all - such memory, after which preg may no longer be used as a compiled - expression. + ciated with the preg structure. The function regfree() frees all such + memory, after which preg may no longer be used as a compiled expres- + sion. AUTHOR @@ -9950,8 +9653,8 @@ AUTHOR REVISION - Last updated: 30 January 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 15 June 2017 + Copyright (c) 1997-2017 University of Cambridge. ------------------------------------------------------------------------------ @@ -10256,8 +9959,7 @@ QUOTING ESCAPED CHARACTERS - This table applies to ASCII and Unicode environments. An unrecognized - escape sequence causes an error. + This table applies to ASCII and Unicode environments. \a alarm, that is, the BEL character (hex 07) \cx "control-x", where x is any ASCII printing character @@ -10269,32 +9971,26 @@ ESCAPED CHARACTERS \0dd character with octal code 0dd \ddd character with octal code ddd, or backreference \o{ddd..} character with octal code ddd.. + \U "U" if PCRE2_ALT_BSUX is set (otherwise is an error) \N{U+hh..} character with Unicode code point hh.. (Unicode mode only) + \uhhhh character with hex code hhhh (if PCRE2_ALT_BSUX is set) \xhh character with hex code hh \x{hh..} character with hex code hh.. - If PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX is set ("ALT_BSUX mode"), the - following are also recognized: - - \U the character "U" - \uhhhh character with hex code hhhh - \u{hh..} character with hex code hh.. but only for EXTRA_ALT_BSUX - - When \x is not followed by {, from zero to two hexadecimal digits are - read, but in ALT_BSUX mode \x must be followed by two hexadecimal dig- - its to be recognized as a hexadecimal escape; otherwise it matches a - literal "x". Likewise, if \u (in ALT_BSUX mode) is not followed by - four hexadecimal digits or (in EXTRA_ALT_BSUX mode) a sequence of hex - digits in curly brackets, it matches a literal "u". - Note that \0dd is always an octal code. The treatment of backslash fol- - lowed by a non-zero digit is complicated; for details see the section - "Non-printing characters" in the pcre2pattern documentation, where - details of escape processing in EBCDIC environments are also given. + lowed by a non-zero digit is complicated; for details see the section + "Non-printing characters" in the pcre2pattern documentation, where + details of escape processing in EBCDIC environments are also given. \N{U+hh..} is synonymous with \x{hh..} in PCRE2 but is not supported in - EBCDIC environments. Note that \N not followed by an opening curly + EBCDIC environments. Note that \N not followed by an opening curly bracket has a different meaning (see below). + When \x is not followed by {, from zero to two hexadecimal digits are + read, but if PCRE2_ALT_BSUX is set, \x must be followed by two hexadec- + imal digits to be recognized as a hexadecimal escape; otherwise it + matches a literal "x". Likewise, if \u (in ALT_BSUX mode) is not fol- + lowed by four hexadecimal digits, it matches a literal "u". + CHARACTER TYPES @@ -10317,14 +10013,14 @@ CHARACTER TYPES \W a "non-word" character \X a Unicode extended grapheme cluster - \C is dangerous because it may leave the current matching point in the + \C is dangerous because it may leave the current matching point in the middle of a UTF-8 or UTF-16 character. The application can lock out the - use of \C by setting the PCRE2_NEVER_BACKSLASH_C option. It is also + use of \C by setting the PCRE2_NEVER_BACKSLASH_C option. It is also possible to build PCRE2 with the use of \C permanently disabled. - By default, \d, \s, and \w match only ASCII characters, even in UTF-8 + By default, \d, \s, and \w match only ASCII characters, even in UTF-8 mode or in the 16-bit and 32-bit libraries. However, if locale-specific - matching is happening, \s and \w may also match characters with code + matching is happening, \s and \w may also match characters with code points in the range 128-255. If the PCRE2_UCP option is set, the behav- iour of these escape sequences is changed to use Unicode properties and they match many more characters. @@ -10393,28 +10089,28 @@ PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P SCRIPT NAMES FOR \p AND \P - Adlam, Ahom, Anatolian_Hieroglyphs, Arabic, Armenian, Avestan, Bali- - nese, Bamum, Bassa_Vah, Batak, Bengali, Bhaiksuki, Bopomofo, Brahmi, - Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Caucasian_Alba- - nian, Chakma, Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, - Cyrillic, Deseret, Devanagari, Dogra, Duployan, Egyptian_Hieroglyphs, - Elbasan, Ethiopic, Georgian, Glagolitic, Gothic, Grantha, Greek, - Gujarati, Gunjala_Gondi, Gurmukhi, Han, Hangul, Hanifi_Rohingya, - Hanunoo, Hatran, Hebrew, Hiragana, Imperial_Aramaic, Inherited, - Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi, Kan- - nada, Katakana, Kayah_Li, Kharoshthi, Khmer, Khojki, Khudawadi, Lao, - Latin, Lepcha, Limbu, Linear_A, Linear_B, Lisu, Lycian, Lydian, Maha- - jani, Makasar, Malayalam, Mandaic, Manichaean, Marchen, Masaram_Gondi, + Adlam, Ahom, Anatolian_Hieroglyphs, Arabic, Armenian, Avestan, Bali- + nese, Bamum, Bassa_Vah, Batak, Bengali, Bhaiksuki, Bopomofo, Brahmi, + Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Caucasian_Alba- + nian, Chakma, Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, + Cyrillic, Deseret, Devanagari, Dogra, Duployan, Egyptian_Hieroglyphs, + Elbasan, Ethiopic, Georgian, Glagolitic, Gothic, Grantha, Greek, + Gujarati, Gunjala_Gondi, Gurmukhi, Han, Hangul, Hanifi_Rohingya, + Hanunoo, Hatran, Hebrew, Hiragana, Imperial_Aramaic, Inherited, + Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi, Kan- + nada, Katakana, Kayah_Li, Kharoshthi, Khmer, Khojki, Khudawadi, Lao, + Latin, Lepcha, Limbu, Linear_A, Linear_B, Lisu, Lycian, Lydian, Maha- + jani, Makasar, Malayalam, Mandaic, Manichaean, Marchen, Masaram_Gondi, Medefaidrin, Meetei_Mayek, Mende_Kikakui, Meroitic_Cursive, - Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro, Multani, Myanmar, - Nabataean, New_Tai_Lue, Newa, Nko, Nushu, Ogham, Ol_Chiki, Old_Hungar- - ian, Old_Italic, Old_North_Arabian, Old_Permic, Old_Persian, Old_Sog- - dian, Old_South_Arabian, Old_Turkic, Oriya, Osage, Osmanya, + Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro, Multani, Myanmar, + Nabataean, New_Tai_Lue, Newa, Nko, Nushu, Ogham, Ol_Chiki, Old_Hungar- + ian, Old_Italic, Old_North_Arabian, Old_Permic, Old_Persian, Old_Sog- + dian, Old_South_Arabian, Old_Turkic, Oriya, Osage, Osmanya, Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa, Phoenician, - Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra, Sharada, Sha- - vian, Siddham, SignWriting, Sinhala, Sogdian, Sora_Sompeng, Soyombo, - Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, - Tai_Viet, Takri, Tamil, Tangut, Telugu, Thaana, Thai, Tibetan, Tifi- + Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra, Sharada, Sha- + vian, Siddham, SignWriting, Sinhala, Sogdian, Sora_Sompeng, Soyombo, + Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, + Tai_Viet, Takri, Tamil, Tangut, Telugu, Thaana, Thai, Tibetan, Tifi- nagh, Tirhuta, Ugaritic, Vai, Warang_Citi, Yi, Zanabazar_Square. @@ -10441,8 +10137,8 @@ CHARACTER CLASSES word same as \w xdigit hexadecimal digit - In PCRE2, POSIX character set names recognize only ASCII characters by - default, but some of them use Unicode properties if PCRE2_UCP is set. + In PCRE2, POSIX character set names recognize only ASCII characters by + default, but some of them use Unicode properties if PCRE2_UCP is set. You can use \Q...\E inside a character class. @@ -10497,23 +10193,18 @@ ALTERNATION CAPTURING - (...) capture group - (?<name>...) named capture group (Perl) - (?'name'...) named capture group (Perl) - (?P<name>...) named capture group (Python) - (?:...) non-capture group - (?|...) non-capture group; reset group numbers for - capture groups in each alternative - - In non-UTF modes, names may contain underscores and ASCII letters and - digits; in UTF modes, any Unicode letters and Unicode decimal digits - are permitted. In both cases, a name must not start with a digit. + (...) capturing group + (?<name>...) named capturing group (Perl) + (?'name'...) named capturing group (Perl) + (?P<name>...) named capturing group (Python) + (?:...) non-capturing group + (?|...) non-capturing group; reset group numbers for + capturing groups in each alternative ATOMIC GROUPS - (?>...) atomic non-capture group - (*atomic:...) atomic non-capture group + (?>...) atomic, non-capturing group COMMENT @@ -10522,7 +10213,7 @@ COMMENT OPTION SETTING - Changes of these options within a group are automatically cancelled at + Changes of these options within a group are automatically cancelled at the end of the group. (?i) caseless @@ -10536,14 +10227,14 @@ OPTION SETTING (?-...) unset option(s) (?^) unset imnsx options - Unsetting x or xx unsets both. Several options may be set at once, and + Unsetting x or xx unsets both. Several options may be set at once, and a mixture of setting and unsetting such as (?i-x) is allowed, but there may be only one hyphen. Setting (but no unsetting) is allowed after (?^ for example (?^in). An option setting may appear at the start of a non- - capture group, for example (?i:...). + capturing group, for example (?i:...). - The following are recognized only at the very start of a pattern or - after one of the newline or \R options with similar syntax. More than + The following are recognized only at the very start of a pattern or + after one of the newline or \R options with similar syntax. More than one of them may appear. For the first three, d is a decimal number. (*LIMIT_DEPTH=d) set the backtracking limit to d @@ -10558,17 +10249,17 @@ OPTION SETTING (*UTF) set appropriate UTF mode for the library in use (*UCP) set PCRE2_UCP (use Unicode properties for \d etc) - Note that LIMIT_DEPTH, LIMIT_HEAP, and LIMIT_MATCH can only reduce the - value of the limits set by the caller of pcre2_match() or - pcre2_dfa_match(), not increase them. LIMIT_RECURSION is an obsolete + Note that LIMIT_DEPTH, LIMIT_HEAP, and LIMIT_MATCH can only reduce the + value of the limits set by the caller of pcre2_match() or + pcre2_dfa_match(), not increase them. LIMIT_RECURSION is an obsolete synonym for LIMIT_DEPTH. The application can lock out the use of (*UTF) - and (*UCP) by setting the PCRE2_NEVER_UTF or PCRE2_NEVER_UCP options, + and (*UCP) by setting the PCRE2_NEVER_UTF or PCRE2_NEVER_UCP options, respectively, at compile time. NEWLINE CONVENTION - These are recognized only at the very start of the pattern or after + These are recognized only at the very start of the pattern or after option settings with a similar syntax. (*CR) carriage return only @@ -10581,7 +10272,7 @@ NEWLINE CONVENTION WHAT \R MATCHES - These are recognized only at the very start of the pattern or after + These are recognized only at the very start of the pattern or after option setting with a similar syntax. (*BSR_ANYCRLF) CR, LF, or CRLF @@ -10590,32 +10281,12 @@ WHAT \R MATCHES LOOKAHEAD AND LOOKBEHIND ASSERTIONS - (?=...) ) - (*pla:...) ) positive lookahead - (*positive_lookahead:...) ) - - (?!...) ) - (*nla:...) ) negative lookahead - (*negative_lookahead:...) ) - - (?<=...) ) - (*plb:...) ) positive lookbehind - (*positive_lookbehind:...) ) + (?=...) positive look ahead + (?!...) negative look ahead + (?<=...) positive look behind + (?<!...) negative look behind - (?<!...) ) - (*nlb:...) ) negative lookbehind - (*negative_lookbehind:...) ) - - Each top-level branch of a lookbehind must be of a fixed length. - - -SCRIPT RUNS - - (*script_run:...) ) script run, can be backtracked into - (*sr:...) ) - - (*atomic_script_run:...) ) atomic script run - (*asr:...) ) + Each top-level branch of a look behind must be of a fixed length. BACKREFERENCES @@ -10637,19 +10308,19 @@ BACKREFERENCES SUBROUTINE REFERENCES (POSSIBLY RECURSIVE) (?R) recurse whole pattern - (?n) call subroutine by absolute number - (?+n) call subroutine by relative number - (?-n) call subroutine by relative number - (?&name) call subroutine by name (Perl) - (?P>name) call subroutine by name (Python) - \g<name> call subroutine by name (Oniguruma) - \g'name' call subroutine by name (Oniguruma) - \g<n> call subroutine by absolute number (Oniguruma) - \g'n' call subroutine by absolute number (Oniguruma) - \g<+n> call subroutine by relative number (PCRE2 extension) - \g'+n' call subroutine by relative number (PCRE2 extension) - \g<-n> call subroutine by relative number (PCRE2 extension) - \g'-n' call subroutine by relative number (PCRE2 extension) + (?n) call subpattern by absolute number + (?+n) call subpattern by relative number + (?-n) call subpattern by relative number + (?&name) call subpattern by name (Perl) + (?P>name) call subpattern by name (Python) + \g<name> call subpattern by name (Oniguruma) + \g'name' call subpattern by name (Oniguruma) + \g<n> call subpattern by absolute number (Oniguruma) + \g'n' call subpattern by absolute number (Oniguruma) + \g<+n> call subpattern by relative number (PCRE2 extension) + \g'+n' call subpattern by relative number (PCRE2 extension) + \g<-n> call subpattern by relative number (PCRE2 extension) + \g'-n' call subpattern by relative number (PCRE2 extension) CONDITIONAL PATTERNS @@ -10666,20 +10337,20 @@ CONDITIONAL PATTERNS (?(R) overall recursion condition (?(Rn) specific numbered group recursion condition (?(R&name) specific named group recursion condition - (?(DEFINE) define groups for reference + (?(DEFINE) define subpattern for reference (?(VERSION[>]=n.m) test PCRE2 version (?(assert) assertion condition - Note the ambiguity of (?(R) and (?(Rn) which might be named reference - conditions or recursion tests. Such a condition is interpreted as a + Note the ambiguity of (?(R) and (?(Rn) which might be named reference + conditions or recursion tests. Such a condition is interpreted as a reference condition if the relevant named group exists. BACKTRACKING CONTROL - All backtracking control verbs may be in the form (*VERB:NAME). For - (*MARK) the name is mandatory, for the others it is optional. (*SKIP) - changes its behaviour if :NAME is present. The others just set a name + All backtracking control verbs may be in the form (*VERB:NAME). For + (*MARK) the name is mandatory, for the others it is optional. (*SKIP) + changes its behaviour if :NAME is present. The others just set a name for passing back to the caller, but this is not a name that (*SKIP) can see. The following act immediately they are reached: @@ -10687,7 +10358,7 @@ BACKTRACKING CONTROL (*FAIL) force backtrack; synonym (*F) (*MARK:NAME) set name to be passed back; synonym (*:NAME) - The following act only when a subsequent match failure causes a back- + The following act only when a subsequent match failure causes a back- track to reach them. They all force a match failure, but they differ in what happens afterwards. Those that advance the start-of-match point do so only if the pattern is not anchored. @@ -10699,7 +10370,7 @@ BACKTRACKING CONTROL (*MARK:NAME); if not found, the (*SKIP) is ignored (*THEN) local failure, backtrack to next alternation - The effect of one of these verbs in a group called as a subroutine is + The effect of one of these verbs in a group called as a subroutine is confined to the subroutine call. @@ -10710,14 +10381,14 @@ CALLOUTS (?C"text") callout with string data The allowed string delimiters are ` ' " ^ % # $ (which are the same for - the start and the end), and the starting delimiter { matched with the - ending delimiter }. To encode the ending delimiter within the string, + the start and the end), and the starting delimiter { matched with the + ending delimiter }. To encode the ending delimiter within the string, double it. SEE ALSO - pcre2pattern(3), pcre2api(3), pcre2callout(3), pcre2matching(3), + pcre2pattern(3), pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2(3). @@ -10730,8 +10401,8 @@ AUTHOR REVISION - Last updated: 11 February 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 02 September 2018 + Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ @@ -10764,73 +10435,66 @@ UNICODE AND UTF SUPPORT UNICODE PROPERTY SUPPORT When PCRE2 is built with Unicode support, the escape sequences \p{..}, - \P{..}, and \X can be used. This is not dependent on the PCRE2_UTF set- - ting. The Unicode properties that can be tested are limited to the - general category properties such as Lu for an upper case letter or Nd - for a decimal number, the Unicode script names such as Arabic or Han, - and the derived properties Any and L&. Full lists are given in the - pcre2pattern and pcre2syntax documentation. Only the short names for - properties are supported. For example, \p{L} matches a letter. Its Perl - synonym, \p{Letter}, is not supported. Furthermore, in Perl, many - properties may optionally be prefixed by "Is", for compatibility with - Perl 5.6. PCRE2 does not support this. + \P{..}, and \X can be used. The Unicode properties that can be tested + are limited to the general category properties such as Lu for an upper + case letter or Nd for a decimal number, the Unicode script names such + as Arabic or Han, and the derived properties Any and L&. Full lists are + given in the pcre2pattern and pcre2syntax documentation. Only the short + names for properties are supported. For example, \p{L} matches a let- + ter. Its Perl synonym, \p{Letter}, is not supported. Furthermore, in + Perl, many properties may optionally be prefixed by "Is", for compati- + bility with Perl 5.6. PCRE2 does not support this. WIDE CHARACTERS AND UTF MODES Code points less than 256 can be specified in patterns by either braced or unbraced hexadecimal escape sequences (for example, \x{b3} or \xb3). - Larger values have to use braced sequences. Unbraced octal code points + Larger values have to use braced sequences. Unbraced octal code points up to \777 are also recognized; larger ones can be coded using \o{...}. - The escape sequence \N{U+<hex digits>} is recognized as another way of - specifying a Unicode character by code point in a UTF mode. It is not + The escape sequence \N{U+<hex digits>} is recognized as another way of + specifying a Unicode character by code point in a UTF mode. It is not allowed in non-UTF modes. - In UTF modes, repeat quantifiers apply to complete UTF characters, not + In UTF modes, repeat quantifiers apply to complete UTF characters, not to individual code units. - In UTF modes, the dot metacharacter matches one UTF character instead + In UTF modes, the dot metacharacter matches one UTF character instead of a single code unit. - In UTF modes, capture group names are not restricted to ASCII, and may - contain any Unicode letters and decimal digits, as well as underscore. - The escape sequence \C can be used to match a single code unit in a UTF mode, but its use can lead to some strange effects because it breaks up multi-unit characters (see the description of \C in the pcre2pattern - documentation). For this reason, there is a build-time option that dis- - ables support for \C completely. There is also a less draconian com- - pile-time option for locking out the use of \C when a pattern is com- - piled. + documentation). - The use of \C is not supported by the alternative matching function + The use of \C is not supported by the alternative matching function pcre2_dfa_match() when in UTF-8 or UTF-16 mode, that is, when a charac- - ter may consist of more than one code unit. The use of \C in these - modes provokes a match-time error. Also, the JIT optimization does not + ter may consist of more than one code unit. The use of \C in these + modes provokes a match-time error. Also, the JIT optimization does not support \C in these modes. If JIT optimization is requested for a UTF-8 - or UTF-16 pattern that contains \C, it will not succeed, and so when + or UTF-16 pattern that contains \C, it will not succeed, and so when pcre2_match() is called, the matching will be carried out by the normal interpretive function. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly test - characters of any code value, but, by default, the characters that - PCRE2 recognizes as digits, spaces, or word characters remain the same - set as in non-UTF mode, all with code points less than 256. This - remains true even when PCRE2 is built to include Unicode support, - because to do otherwise would slow down matching in many common cases. - Note that this also applies to \b and \B, because they are defined in - terms of \w and \W. If you want to test for a wider sense of, say, - "digit", you can use explicit Unicode property tests such as \p{Nd}. - Alternatively, if you set the PCRE2_UCP option, the way that the char- - acter escapes work is changed so that Unicode properties are used to + characters of any code value, but, by default, the characters that + PCRE2 recognizes as digits, spaces, or word characters remain the same + set as in non-UTF mode, all with code points less than 256. This + remains true even when PCRE2 is built to include Unicode support, + because to do otherwise would slow down matching in many common cases. + Note that this also applies to \b and \B, because they are defined in + terms of \w and \W. If you want to test for a wider sense of, say, + "digit", you can use explicit Unicode property tests such as \p{Nd}. + Alternatively, if you set the PCRE2_UCP option, the way that the char- + acter escapes work is changed so that Unicode properties are used to determine which characters match. There are more details in the section on generic character types in the pcre2pattern documentation. - Similarly, characters that match the POSIX named character classes are + Similarly, characters that match the POSIX named character classes are all low-valued characters, unless the PCRE2_UCP option is set. - However, the special horizontal and vertical white space matching + However, the special horizontal and vertical white space matching escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char- acters, whether or not PCRE2_UCP is set. @@ -10840,156 +10504,35 @@ CASE-EQUIVALENCE IN UTF MODES Case-insensitive matching in a UTF mode makes use of Unicode properties except for characters whose code points are less than 128 and that have at most two case-equivalent values. For these, a direct table lookup is - used for speed. A few Unicode characters such as Greek sigma have more + used for speed. A few Unicode characters such as Greek sigma have more than two code points that are case-equivalent, and these are treated as such. -SCRIPT RUNS - - The pattern constructs (*script_run:...) and (*atomic_script_run:...), - with synonyms (*sr:...) and (*asr:...), verify that the string matched - within the parentheses is a script run. In concept, a script run is a - sequence of characters that are all from the same Unicode script. How- - ever, because some scripts are commonly used together, and because some - diacritical and other marks are used with multiple scripts, it is not - that simple. - - Every Unicode character has a Script property, mostly with a value cor- - responding to the name of a script, such as Latin, Greek, or Cyrillic. - There are also three special values: - - "Unknown" is used for code points that have not been assigned, and also - for the surrogate code points. In the PCRE2 32-bit library, characters - whose code points are greater than the Unicode maximum (U+10FFFF), - which are accessible only in non-UTF mode, are assigned the Unknown - script. - - "Common" is used for characters that are used with many scripts. These - include punctuation, emoji, mathematical, musical, and currency sym- - bols, and the ASCII digits 0 to 9. - - "Inherited" is used for characters such as diacritical marks that mod- - ify a previous character. These are considered to take on the script of - the character that they modify. - - Some Inherited characters are used with many scripts, but many of them - are only normally used with a small number of scripts. For example, - U+102E0 (Coptic Epact thousands mark) is used only with Arabic and Cop- - tic. In order to make it possible to check this, a Unicode property - called Script Extension exists. Its value is a list of scripts that - apply to the character. For the majority of characters, the list con- - tains just one script, the same one as the Script property. However, - for characters such as U+102E0 more than one Script is listed. There - are also some Common characters that have a single, non-Common script - in their Script Extension list. - - The next section describes the basic rules for deciding whether a given - string of characters is a script run. Note, however, that there are - some special cases involving the Chinese Han script, and an additional - constraint for decimal digits. These are covered in subsequent sec- - tions. - - Basic script run rules - - A string that is less than two characters long is a script run. This is - the only case in which an Unknown character can be part of a script - run. Longer strings are checked using only the Script Extensions prop- - erty, not the basic Script property. - - If a character's Script Extension property is the single value "Inher- - ited", it is always accepted as part of a script run. This is also true - for the property "Common", subject to the checking of decimal digits - described below. All the remaining characters in a script run must have - at least one script in common in their Script Extension lists. In set- - theoretic terminology, the intersection of all the sets of scripts must - not be empty. - - A simple example is an Internet name such as "google.com". The letters - are all in the Latin script, and the dot is Common, so this string is a - script run. However, the Cyrillic letter "o" looks exactly the same as - the Latin "o"; a string that looks the same, but with Cyrillic "o"s is - not a script run. - - More interesting examples involve characters with more than one script - in their Script Extension. Consider the following characters: - - U+060C Arabic comma - U+06D4 Arabic full stop - - The first has the Script Extension list Arabic, Hanifi Rohingya, Syr- - iac, and Thaana; the second has just Arabic and Hanifi Rohingya. Both - of them could appear in script runs of either Arabic or Hanifi - Rohingya. The first could also appear in Syriac or Thaana script runs, - but the second could not. - - The Chinese Han script - - The Chinese Han script is commonly used in conjunction with other - scripts for writing certain languages. Japanese uses the Hiragana and - Katakana scripts together with Han; Korean uses Hangul and Han; Tai- - wanese Mandarin uses Bopomofo and Han. These three combinations are - treated as special cases when checking script runs and are, in effect, - "virtual scripts". Thus, a script run may contain a mixture of Hira- - gana, Katakana, and Han, or a mixture of Hangul and Han, or a mixture - of Bopomofo and Han, but not, for example, a mixture of Hangul and - Bopomofo and Han. PCRE2 (like Perl) follows Unicode's Technical Stan- - dard 39 ("Unicode Security Mechanisms", http://uni- - code.org/reports/tr39/) in allowing such mixtures. - - Decimal digits - - Unicode contains many sets of 10 decimal digits in different scripts, - and some scripts (including the Common script) contain more than one - set. Some of these decimal digits them are visually indistinguishable - from the common ASCII digits. In addition to the script checking - described above, if a script run contains any decimal digits, they must - all come from the same set of 10 adjacent characters. - - VALIDITY OF UTF STRINGS - When the PCRE2_UTF option is set, the strings passed as patterns and + When the PCRE2_UTF option is set, the strings passed as patterns and subjects are (by default) checked for validity on entry to the relevant - functions. If an invalid UTF string is passed, an negative error code - is returned. The code unit offset to the offending character can be - extracted from the match data block by calling pcre2_get_startchar(), + functions. If an invalid UTF string is passed, an negative error code + is returned. The code unit offset to the offending character can be + extracted from the match data block by calling pcre2_get_startchar(), which is used for this purpose after a UTF error. - In some situations, you may already know that your strings are valid, - and therefore want to skip these checks in order to improve perfor- - mance, for example in the case of a long subject string that is being - scanned repeatedly. If you set the PCRE2_NO_UTF_CHECK option at com- - pile time or at match time, PCRE2 assumes that the pattern or subject - it is given (respectively) contains only valid UTF code unit sequences. - - If you pass an invalid UTF string when PCRE2_NO_UTF_CHECK is set, the - result is usually undefined and your program may crash or loop indefi- - nitely. There is, however, one mode of matching that can handle invalid - UTF subject strings. This is matching via the JIT optimization using - the PCRE2_JIT_INVALID_UTF option when calling pcre2_jit_compile(). For - details, see the pcre2jit documentation. - - Passing PCRE2_NO_UTF_CHECK to pcre2_compile() just disables the check - for the pattern; it does not also apply to subject strings. If you want - to disable the check for a subject string you must pass this same - option to pcre2_match() or pcre2_dfa_match(). - UTF-16 and UTF-32 strings can indicate their endianness by special code knows as a byte-order mark (BOM). The PCRE2 functions do not handle this, expecting strings to be in host byte order. - Unless PCRE2_NO_UTF_CHECK is set, a UTF string is checked before any - other processing takes place. In the case of pcre2_match() and - pcre2_dfa_match() calls with a non-zero starting offset, the check is - applied only to that part of the subject that could be inspected during - matching, and there is a check that the starting offset points to the - first code unit of a character or to the end of the subject. If there - are no lookbehind assertions in the pattern, the check starts at the - starting offset. Otherwise, it starts at the length of the longest - lookbehind before the starting offset, or at the start of the subject - if there are not that many characters before the starting offset. Note - that the sequences \b and \B are one-character lookbehinds. + A UTF string is checked before any other processing takes place. In the + case of pcre2_match() and pcre2_dfa_match() calls with a non-zero + starting offset, the check is applied only to that part of the subject + that could be inspected during matching, and there is a check that the + starting offset points to the first code unit of a character or to the + end of the subject. If there are no lookbehind assertions in the pat- + tern, the check starts at the starting offset. Otherwise, it starts at + the length of the longest lookbehind before the starting offset, or at + the start of the subject if there are not that many characters before + the starting offset. Note that the sequences \b and \B are one-charac- + ter lookbehinds. In addition to checking the format of the string, there is a check to ensure that all code points lie in the range U+0 to U+10FFFF, excluding @@ -11004,10 +10547,25 @@ VALIDITY OF UTF STRINGS other words, the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and UTF-32.) - Setting PCRE2_NO_UTF_CHECK at compile time does not disable the error - that is given if an escape sequence for an invalid Unicode code point - is encountered in the pattern. If you want to allow escape sequences - such as \x{d800} (a surrogate code point) you can set the + In some situations, you may already know that your strings are valid, + and therefore want to skip these checks in order to improve perfor- + mance, for example in the case of a long subject string that is being + scanned repeatedly. If you set the PCRE2_NO_UTF_CHECK option at com- + pile time or at match time, PCRE2 assumes that the pattern or subject + it is given (respectively) contains only valid UTF code unit sequences. + + Passing PCRE2_NO_UTF_CHECK to pcre2_compile() just disables the check + for the pattern; it does not also apply to subject strings. If you want + to disable the check for a subject string you must pass this option to + pcre2_match() or pcre2_dfa_match(). + + If you pass an invalid UTF string when PCRE2_NO_UTF_CHECK is set, the + result is undefined and your program may crash or loop indefinitely. + + Note that setting PCRE2_NO_UTF_CHECK at compile time does not disable + the error that is given if an escape sequence for an invalid Unicode + code point is encountered in the pattern. If you want to allow escape + sequences such as \x{d800} (a surrogate code point) you can set the PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extra option. However, this is pos- sible only in UTF-8 and UTF-32 modes, because these values are not rep- resentable in UTF-16. @@ -11022,10 +10580,10 @@ VALIDITY OF UTF STRINGS PCRE2_ERROR_UTF8_ERR4 PCRE2_ERROR_UTF8_ERR5 - The string ends with a truncated UTF-8 character; the code specifies - how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 - characters to be no longer than 4 bytes, the encoding scheme (origi- - nally defined by RFC 2279) allows for up to 6 bytes, and this is + The string ends with a truncated UTF-8 character; the code specifies + how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 + characters to be no longer than 4 bytes, the encoding scheme (origi- + nally defined by RFC 2279) allows for up to 6 bytes, and this is checked first; hence the possibility of 4 or 5 missing bytes. PCRE2_ERROR_UTF8_ERR6 @@ -11035,24 +10593,24 @@ VALIDITY OF UTF STRINGS PCRE2_ERROR_UTF8_ERR10 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of - the character do not have the binary value 0b10 (that is, either the + the character do not have the binary value 0b10 (that is, either the most significant bit is 0, or the next bit is 1). PCRE2_ERROR_UTF8_ERR11 PCRE2_ERROR_UTF8_ERR12 - A character that is valid by the RFC 2279 rules is either 5 or 6 bytes + A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long; these code points are excluded by RFC 3629. PCRE2_ERROR_UTF8_ERR13 - A 4-byte character has a value greater than 0x10fff; these code points + A 4-byte character has a value greater than 0x10fff; these code points are excluded by RFC 3629. PCRE2_ERROR_UTF8_ERR14 - A 3-byte character has a value in the range 0xd800 to 0xdfff; this - range of code points are reserved by RFC 3629 for use with UTF-16, and + A 3-byte character has a value in the range 0xd800 to 0xdfff; this + range of code points are reserved by RFC 3629 for use with UTF-16, and so are excluded from UTF-8. PCRE2_ERROR_UTF8_ERR15 @@ -11061,26 +10619,26 @@ VALIDITY OF UTF STRINGS PCRE2_ERROR_UTF8_ERR18 PCRE2_ERROR_UTF8_ERR19 - A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes - for a value that can be represented by fewer bytes, which is invalid. - For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- + A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes + for a value that can be represented by fewer bytes, which is invalid. + For example, the two bytes 0xc0, 0xae give the value 0x2e, whose cor- rect coding uses just one byte. PCRE2_ERROR_UTF8_ERR20 The two most significant bits of the first byte of a character have the - binary value 0b10 (that is, the most significant bit is 1 and the sec- - ond is 0). Such a byte can only validly occur as the second or subse- + binary value 0b10 (that is, the most significant bit is 1 and the sec- + ond is 0). Such a byte can only validly occur as the second or subse- quent byte of a multi-byte character. PCRE2_ERROR_UTF8_ERR21 - The first byte of a character has the value 0xfe or 0xff. These values + The first byte of a character has the value 0xfe or 0xff. These values can never occur in a valid UTF-8 string. Errors in UTF-16 strings - The following negative error codes are given for invalid UTF-16 + The following negative error codes are given for invalid UTF-16 strings: PCRE2_ERROR_UTF16_ERR1 Missing low surrogate at end of string @@ -11090,7 +10648,7 @@ VALIDITY OF UTF STRINGS Errors in UTF-32 strings - The following negative error codes are given for invalid UTF-32 + The following negative error codes are given for invalid UTF-32 strings: PCRE2_ERROR_UTF32_ERR1 Surrogate character (0xd800 to 0xdfff) @@ -11106,8 +10664,8 @@ AUTHOR REVISION - Last updated: 06 March 2019 - Copyright (c) 1997-2019 University of Cambridge. + Last updated: 02 September 2018 + Copyright (c) 1997-2018 University of Cambridge. ------------------------------------------------------------------------------ |