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diff --git a/share/cmake-3.17/Help/command/if.rst b/share/cmake-3.17/Help/command/if.rst new file mode 100644 index 0000000..be992df --- /dev/null +++ b/share/cmake-3.17/Help/command/if.rst @@ -0,0 +1,280 @@ +if +-- + +Conditionally execute a group of commands. + +Synopsis +^^^^^^^^ + +.. code-block:: cmake + + if(<condition>) + <commands> + elseif(<condition>) # optional block, can be repeated + <commands> + else() # optional block + <commands> + endif() + +Evaluates the ``condition`` argument of the ``if`` clause according to the +`Condition syntax`_ described below. If the result is true, then the +``commands`` in the ``if`` block are executed. +Otherwise, optional ``elseif`` blocks are processed in the same way. +Finally, if no ``condition`` is true, ``commands`` in the optional ``else`` +block are executed. + +Per legacy, the :command:`else` and :command:`endif` commands admit +an optional ``<condition>`` argument. +If used, it must be a verbatim +repeat of the argument of the opening +``if`` command. + +.. _`Condition Syntax`: + +Condition Syntax +^^^^^^^^^^^^^^^^ + +The following syntax applies to the ``condition`` argument of +the ``if``, ``elseif`` and :command:`while` clauses. + +Compound conditions are evaluated in the following order of precedence: +Innermost parentheses are evaluated first. Next come unary tests such +as ``EXISTS``, ``COMMAND``, and ``DEFINED``. Then binary tests such as +``EQUAL``, ``LESS``, ``LESS_EQUAL``, ``GREATER``, ``GREATER_EQUAL``, +``STREQUAL``, ``STRLESS``, ``STRLESS_EQUAL``, ``STRGREATER``, +``STRGREATER_EQUAL``, ``VERSION_EQUAL``, ``VERSION_LESS``, +``VERSION_LESS_EQUAL``, ``VERSION_GREATER``, ``VERSION_GREATER_EQUAL``, +and ``MATCHES``. Then the boolean operators in the order ``NOT``, ``AND``, +and finally ``OR``. + +Possible conditions are: + +``if(<constant>)`` + True if the constant is ``1``, ``ON``, ``YES``, ``TRUE``, ``Y``, + or a non-zero number. False if the constant is ``0``, ``OFF``, + ``NO``, ``FALSE``, ``N``, ``IGNORE``, ``NOTFOUND``, the empty string, + or ends in the suffix ``-NOTFOUND``. Named boolean constants are + case-insensitive. If the argument is not one of these specific + constants, it is treated as a variable or string and the following + signature is used. + +``if(<variable|string>)`` + True if given a variable that is defined to a value that is not a false + constant. False otherwise. (Note macro arguments are not variables.) + +``if(NOT <condition>)`` + True if the condition is not true. + +``if(<cond1> AND <cond2>)`` + True if both conditions would be considered true individually. + +``if(<cond1> OR <cond2>)`` + True if either condition would be considered true individually. + +``if(COMMAND command-name)`` + True if the given name is a command, macro or function that can be + invoked. + +``if(POLICY policy-id)`` + True if the given name is an existing policy (of the form ``CMP<NNNN>``). + +``if(TARGET target-name)`` + True if the given name is an existing logical target name created + by a call to the :command:`add_executable`, :command:`add_library`, + or :command:`add_custom_target` command that has already been invoked + (in any directory). + +``if(TEST test-name)`` + True if the given name is an existing test name created by the + :command:`add_test` command. + +``if(EXISTS path-to-file-or-directory)`` + True if the named file or directory exists. Behavior is well-defined + only for full paths. Resolves symbolic links, i.e. if the named file or + directory is a symbolic link, returns true if the target of the + symbolic link exists. + +``if(file1 IS_NEWER_THAN file2)`` + True if ``file1`` is newer than ``file2`` or if one of the two files doesn't + exist. Behavior is well-defined only for full paths. If the file + time stamps are exactly the same, an ``IS_NEWER_THAN`` comparison returns + true, so that any dependent build operations will occur in the event + of a tie. This includes the case of passing the same file name for + both file1 and file2. + +``if(IS_DIRECTORY path-to-directory)`` + True if the given name is a directory. Behavior is well-defined only + for full paths. + +``if(IS_SYMLINK file-name)`` + True if the given name is a symbolic link. Behavior is well-defined + only for full paths. + +``if(IS_ABSOLUTE path)`` + True if the given path is an absolute path. + +``if(<variable|string> MATCHES regex)`` + True if the given string or variable's value matches the given regular + condition. See :ref:`Regex Specification` for regex format. + ``()`` groups are captured in :variable:`CMAKE_MATCH_<n>` variables. + +``if(<variable|string> LESS <variable|string>)`` + True if the given string or variable's value is a valid number and less + than that on the right. + +``if(<variable|string> GREATER <variable|string>)`` + True if the given string or variable's value is a valid number and greater + than that on the right. + +``if(<variable|string> EQUAL <variable|string>)`` + True if the given string or variable's value is a valid number and equal + to that on the right. + +``if(<variable|string> LESS_EQUAL <variable|string>)`` + True if the given string or variable's value is a valid number and less + than or equal to that on the right. + +``if(<variable|string> GREATER_EQUAL <variable|string>)`` + True if the given string or variable's value is a valid number and greater + than or equal to that on the right. + +``if(<variable|string> STRLESS <variable|string>)`` + True if the given string or variable's value is lexicographically less + than the string or variable on the right. + +``if(<variable|string> STRGREATER <variable|string>)`` + True if the given string or variable's value is lexicographically greater + than the string or variable on the right. + +``if(<variable|string> STREQUAL <variable|string>)`` + True if the given string or variable's value is lexicographically equal + to the string or variable on the right. + +``if(<variable|string> STRLESS_EQUAL <variable|string>)`` + True if the given string or variable's value is lexicographically less + than or equal to the string or variable on the right. + +``if(<variable|string> STRGREATER_EQUAL <variable|string>)`` + True if the given string or variable's value is lexicographically greater + than or equal to the string or variable on the right. + +``if(<variable|string> VERSION_LESS <variable|string>)`` + Component-wise integer version number comparison (version format is + ``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero). + Any non-integer version component or non-integer trailing part of a version + component effectively truncates the string at that point. + +``if(<variable|string> VERSION_GREATER <variable|string>)`` + Component-wise integer version number comparison (version format is + ``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero). + Any non-integer version component or non-integer trailing part of a version + component effectively truncates the string at that point. + +``if(<variable|string> VERSION_EQUAL <variable|string>)`` + Component-wise integer version number comparison (version format is + ``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero). + Any non-integer version component or non-integer trailing part of a version + component effectively truncates the string at that point. + +``if(<variable|string> VERSION_LESS_EQUAL <variable|string>)`` + Component-wise integer version number comparison (version format is + ``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero). + Any non-integer version component or non-integer trailing part of a version + component effectively truncates the string at that point. + +``if(<variable|string> VERSION_GREATER_EQUAL <variable|string>)`` + Component-wise integer version number comparison (version format is + ``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero). + Any non-integer version component or non-integer trailing part of a version + component effectively truncates the string at that point. + +``if(<variable|string> IN_LIST <variable>)`` + True if the given element is contained in the named list variable. + +``if(DEFINED <name>|CACHE{<name>}|ENV{<name>})`` + True if a variable, cache variable or environment variable + with given ``<name>`` is defined. The value of the variable + does not matter. Note that macro arguments are not variables. + +``if((condition) AND (condition OR (condition)))`` + The conditions inside the parenthesis are evaluated first and then + the remaining condition is evaluated as in the previous examples. + Where there are nested parenthesis the innermost are evaluated as part + of evaluating the condition that contains them. + +Variable Expansion +^^^^^^^^^^^^^^^^^^ + +The if command was written very early in CMake's history, predating +the ``${}`` variable evaluation syntax, and for convenience evaluates +variables named by its arguments as shown in the above signatures. +Note that normal variable evaluation with ``${}`` applies before the if +command even receives the arguments. Therefore code like + +.. code-block:: cmake + + set(var1 OFF) + set(var2 "var1") + if(${var2}) + +appears to the if command as + +.. code-block:: cmake + + if(var1) + +and is evaluated according to the ``if(<variable>)`` case documented +above. The result is ``OFF`` which is false. However, if we remove the +``${}`` from the example then the command sees + +.. code-block:: cmake + + if(var2) + +which is true because ``var2`` is defined to ``var1`` which is not a false +constant. + +Automatic evaluation applies in the other cases whenever the +above-documented condition syntax accepts ``<variable|string>``: + +* The left hand argument to ``MATCHES`` is first checked to see if it is + a defined variable, if so the variable's value is used, otherwise the + original value is used. + +* If the left hand argument to ``MATCHES`` is missing it returns false + without error + +* Both left and right hand arguments to ``LESS``, ``GREATER``, ``EQUAL``, + ``LESS_EQUAL``, and ``GREATER_EQUAL``, are independently tested to see if + they are defined variables, if so their defined values are used otherwise + the original value is used. + +* Both left and right hand arguments to ``STRLESS``, ``STRGREATER``, + ``STREQUAL``, ``STRLESS_EQUAL``, and ``STRGREATER_EQUAL`` are independently + tested to see if they are defined variables, if so their defined values are + used otherwise the original value is used. + +* Both left and right hand arguments to ``VERSION_LESS``, + ``VERSION_GREATER``, ``VERSION_EQUAL``, ``VERSION_LESS_EQUAL``, and + ``VERSION_GREATER_EQUAL`` are independently tested to see if they are defined + variables, if so their defined values are used otherwise the original value + is used. + +* The right hand argument to ``NOT`` is tested to see if it is a boolean + constant, if so the value is used, otherwise it is assumed to be a + variable and it is dereferenced. + +* The left and right hand arguments to ``AND`` and ``OR`` are independently + tested to see if they are boolean constants, if so they are used as + such, otherwise they are assumed to be variables and are dereferenced. + +To prevent ambiguity, potential variable or keyword names can be +specified in a :ref:`Quoted Argument` or a :ref:`Bracket Argument`. +A quoted or bracketed variable or keyword will be interpreted as a +string and not dereferenced or interpreted. +See policy :policy:`CMP0054`. + +There is no automatic evaluation for environment or cache +:ref:`Variable References`. Their values must be referenced as +``$ENV{<name>}`` or ``$CACHE{<name>}`` wherever the above-documented +condition syntax accepts ``<variable|string>``. |