212 lines
7.8 KiB
ReStructuredText
212 lines
7.8 KiB
ReStructuredText
if
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--
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Conditionally execute a group of commands.
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.. code-block:: cmake
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if(expression)
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# then section.
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COMMAND1(ARGS ...)
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COMMAND2(ARGS ...)
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...
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elseif(expression2)
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# elseif section.
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COMMAND1(ARGS ...)
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COMMAND2(ARGS ...)
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...
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else(expression)
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# else section.
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COMMAND1(ARGS ...)
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COMMAND2(ARGS ...)
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...
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endif(expression)
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Evaluates the given expression. If the result is true, the commands
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in the THEN section are invoked. Otherwise, the commands in the else
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section are invoked. The elseif and else sections are optional. You
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may have multiple elseif clauses. Note that the expression in the
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else and endif clause is optional. Long expressions can be used and
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there is a traditional order of precedence. Parenthetical expressions
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are evaluated first followed by unary tests such as ``EXISTS``,
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``COMMAND``, and ``DEFINED``. Then any binary tests such as
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``EQUAL``, ``LESS``, ``GREATER``, ``STRLESS``, ``STRGREATER``,
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``STREQUAL``, and ``MATCHES`` will be evaluated. Then boolean ``NOT``
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operators and finally boolean ``AND`` and then ``OR`` operators will
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be evaluated.
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Possible expressions are:
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``if(<constant>)``
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True if the constant is ``1``, ``ON``, ``YES``, ``TRUE``, ``Y``,
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or a non-zero number. False if the constant is ``0``, ``OFF``,
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``NO``, ``FALSE``, ``N``, ``IGNORE``, ``NOTFOUND``, the empty string,
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or ends in the suffix ``-NOTFOUND``. Named boolean constants are
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case-insensitive. If the argument is not one of these specific
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constants, it is treated as a variable or string and the following
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signature is used.
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``if(<variable|string>)``
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True if given a variable that is defined to a value that is not a false
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constant. False otherwise. (Note macro arguments are not variables.)
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``if(NOT <expression>)``
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True if the expression is not true.
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``if(<expr1> AND <expr2>)``
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True if both expressions would be considered true individually.
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``if(<expr1> OR <expr2>)``
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True if either expression would be considered true individually.
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``if(COMMAND command-name)``
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True if the given name is a command, macro or function that can be
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invoked.
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``if(POLICY policy-id)``
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True if the given name is an existing policy (of the form ``CMP<NNNN>``).
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``if(TARGET target-name)``
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True if the given name is an existing logical target name such as those
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created by the :command:`add_executable`, :command:`add_library`, or
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:command:`add_custom_target` commands.
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``if(EXISTS path-to-file-or-directory)``
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True if the named file or directory exists. Behavior is well-defined
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only for full paths.
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``if(file1 IS_NEWER_THAN file2)``
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True if file1 is newer than file2 or if one of the two files doesn't
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exist. Behavior is well-defined only for full paths. If the file
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time stamps are exactly the same, an ``IS_NEWER_THAN`` comparison returns
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true, so that any dependent build operations will occur in the event
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of a tie. This includes the case of passing the same file name for
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both file1 and file2.
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``if(IS_DIRECTORY path-to-directory)``
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True if the given name is a directory. Behavior is well-defined only
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for full paths.
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``if(IS_SYMLINK file-name)``
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True if the given name is a symbolic link. Behavior is well-defined
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only for full paths.
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``if(IS_ABSOLUTE path)``
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True if the given path is an absolute path.
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``if(<variable|string> MATCHES regex)``
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True if the given string or variable's value matches the given regular
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expression.
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``if(<variable|string> LESS <variable|string>)``
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True if the given string or variable's value is a valid number and less
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than that on the right.
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``if(<variable|string> GREATER <variable|string>)``
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True if the given string or variable's value is a valid number and greater
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than that on the right.
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``if(<variable|string> EQUAL <variable|string>)``
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True if the given string or variable's value is a valid number and equal
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to that on the right.
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``if(<variable|string> STRLESS <variable|string>)``
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True if the given string or variable's value is lexicographically less
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than the string or variable on the right.
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``if(<variable|string> STRGREATER <variable|string>)``
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True if the given string or variable's value is lexicographically greater
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than the string or variable on the right.
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``if(<variable|string> STREQUAL <variable|string>)``
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True if the given string or variable's value is lexicographically equal
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to the string or variable on the right.
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``if(<variable|string> VERSION_LESS <variable|string>)``
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Component-wise integer version number comparison (version format is
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``major[.minor[.patch[.tweak]]]``).
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``if(<variable|string> VERSION_EQUAL <variable|string>)``
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Component-wise integer version number comparison (version format is
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``major[.minor[.patch[.tweak]]]``).
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``if(<variable|string> VERSION_GREATER <variable|string>)``
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Component-wise integer version number comparison (version format is
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``major[.minor[.patch[.tweak]]]``).
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``if(<variable|string> IN_LIST <variable>)``
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True if the given element is contained in the named list variable.
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``if(DEFINED <variable>)``
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True if the given variable is defined. It does not matter if the
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variable is true or false just if it has been set. (Note macro
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arguments are not variables.)
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``if((expression) AND (expression OR (expression)))``
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The expressions inside the parenthesis are evaluated first and then
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the remaining expression is evaluated as in the previous examples.
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Where there are nested parenthesis the innermost are evaluated as part
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of evaluating the expression that contains them.
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The if command was written very early in CMake's history, predating
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the ``${}`` variable evaluation syntax, and for convenience evaluates
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variables named by its arguments as shown in the above signatures.
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Note that normal variable evaluation with ``${}`` applies before the if
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command even receives the arguments. Therefore code like::
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set(var1 OFF)
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set(var2 "var1")
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if(${var2})
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appears to the if command as::
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if(var1)
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and is evaluated according to the ``if(<variable>)`` case documented
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above. The result is ``OFF`` which is false. However, if we remove the
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``${}`` from the example then the command sees::
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if(var2)
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which is true because ``var2`` is defined to "var1" which is not a false
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constant.
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Automatic evaluation applies in the other cases whenever the
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above-documented signature accepts ``<variable|string>``:
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* The left hand argument to ``MATCHES`` is first checked to see if it is
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a defined variable, if so the variable's value is used, otherwise the
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original value is used.
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* If the left hand argument to ``MATCHES`` is missing it returns false
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without error
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* Both left and right hand arguments to ``LESS``, ``GREATER``, and
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``EQUAL`` are independently tested to see if they are defined
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variables, if so their defined values are used otherwise the original
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value is used.
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* Both left and right hand arguments to ``STRLESS``, ``STREQUAL``, and
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``STRGREATER`` are independently tested to see if they are defined
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variables, if so their defined values are used otherwise the original
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value is used.
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* Both left and right hand arguments to ``VERSION_LESS``,
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``VERSION_EQUAL``, and ``VERSION_GREATER`` are independently tested
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to see if they are defined variables, if so their defined values are
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used otherwise the original value is used.
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* The right hand argument to ``NOT`` is tested to see if it is a boolean
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constant, if so the value is used, otherwise it is assumed to be a
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variable and it is dereferenced.
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* The left and right hand arguments to ``AND`` and ``OR`` are independently
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tested to see if they are boolean constants, if so they are used as
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such, otherwise they are assumed to be variables and are dereferenced.
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To prevent ambiguity, potential variable or keyword names can be
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specified in a :ref:`Quoted Argument` or a :ref:`Bracket Argument`.
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A quoted or bracketed variable or keyword will be interpreted as a
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string and not dereferenced or interpreted.
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See policy :policy:`CMP0054`.
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