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Diffstat (limited to 'BUGS')
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@@ -0,0 +1,133 @@ +* ABOUT BUGS + +Before reporting a bug, please check the list of known bugs +and the list of oft-reported non-bugs (below). + +Bugs and comments may be sent to bonzini@gnu.org; please +include in the Subject: header the first line of the output of +``sed --version''. + +Please do not send a bug report like this: + + [while building frobme-1.3.4] + $ configure + sed: file sedscr line 1: Unknown option to 's' + +If sed doesn't configure your favorite package, take a few extra +minutes to identify the specific problem and make a stand-alone test +case. + +A stand-alone test case includes all the data necessary to perform the +test, and the specific invocation of sed that causes the problem. The +smaller a stand-alone test case is, the better. A test case should +not involve something as far removed from sed as ``try to configure +frobme-1.3.4''. Yes, that is in principle enough information to look +for the bug, but that is not a very practical prospect. + + + +* NON-BUGS + +`N' command on the last line + + Most versions of sed exit without printing anything when the `N' + command is issued on the last line of a file. GNU sed instead + prints pattern space before exiting unless of course the `-n' + command switch has been specified. More information on the reason + behind this choice can be found in the Info manual. + + +regex syntax clashes (problems with backslashes) + + sed uses the Posix basic regular expression syntax. According to + the standard, the meaning of some escape sequences is undefined in + this syntax; notable in the case of GNU sed are `\|', `\+', `\?', + `\`', `\'', `\<', `\>', `\b', `\B', `\w', and `\W'. + + As in all GNU programs that use Posix basic regular expressions, sed + interprets these escape sequences as meta-characters. So, `x\+' + matches one or more occurrences of `x'. `abc\|def' matches either + `abc' or `def'. + + This syntax may cause problems when running scripts written for other + seds. Some sed programs have been written with the assumption that + `\|' and `\+' match the literal characters `|' and `+'. Such scripts + must be modified by removing the spurious backslashes if they are to + be used with recent versions of sed (not only GNU sed). + + On the other hand, some scripts use `s|abc\|def||g' to remove occurrences + of _either_ `abc' or `def'. While this worked until sed 4.0.x, newer + versions interpret this as removing the string `abc|def'. This is + again undefined behavior according to POSIX, but this interpretation + is arguably more robust: the older one, for example, required that + the regex matcher parsed `\/' as `/' in the common case of escaping + a slash, which is again undefined behavior; the new behavior avoids + this, and this is good because the regex matcher is only partially + under our control. + + In addition, GNU sed supports several escape characters (some of + which are multi-character) to insert non-printable characters + in scripts (`\a', `\c', `\d', `\o', `\r', `\t', `\v', `\x'). These + can cause similar problems with scripts written for other seds. + + +-i clobbers read-only files + + In short, `sed d -i' will let one delete the contents of + a read-only file, and in general the `-i' option will let + one clobber protected files. This is not a bug, but rather a + consequence of how the Unix filesystem works. + + The permissions on a file say what can happen to the data + in that file, while the permissions on a directory say what can + happen to the list of files in that directory. `sed -i' + will not ever open for writing a file that is already on disk, + rather, it will work on a temporary file that is finally renamed + to the original name: if you rename or delete files, you're actually + modifying the contents of the directory, so the operation depends on + the permissions of the directory, not of the file). For this same + reason, sed will not let one use `-i' on a writeable file in a + read-only directory, and will break hard or symbolic links when + `-i' is used on such a file. + + +`0a' does not work (gives an error) + + There is no line 0. 0 is a special address that is only used to treat + addresses like `0,/RE/' as active when the script starts: if you + write `1,/abc/d' and the first line includes the word `abc', then + that match would be ignored because address ranges must span at least + two lines (barring the end of the file); but what you probably wanted is + to delete every line up to the first one including `abc', and this + is obtained with `0,/abc/d'. + + +`[a-z]' is case insensitive +`s/.*//' does not clear pattern space + + You are encountering problems with locales. POSIX mandates that `[a-z]' + uses the current locale's collation order -- in C parlance, that means + strcoll(3) instead of strcmp(3). Some locales have a case insensitive + strcoll, others don't. + + Another problem is that [a-z] tries to use collation symbols. This + only happens if you are on the GNU system, using GNU libc's regular + expression matcher instead of compiling the one supplied with GNU sed. + In a Danish locale, for example, the regular expression `^[a-z]$' + matches the string `aa', because `aa' is a single collating symbol that + comes after `a' and before `b'; `ll' behaves similarly in Spanish + locales, or `ij' in Dutch locales. + + Another common localization-related problem happens if your input stream + includes invalid multibyte sequences. POSIX mandates that such + sequences are _not_ matched by `.', so that `s/.*//' will not clear + pattern space as you would expect. In fact, there is no way to clear + sed's buffers in the middle of the script in most multibyte locales + (including UTF-8 locales). For this reason, GNU sed provides a `z' + command (for `zap') as an extension. + + However, to work around both of these problems, which may cause bugs + in shell scripts, you can set the LC_ALL environment variable to `C', + or set the locale on a more fine-grained basis with the other LC_* + environment variables. + |