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460 lines
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ReStructuredText
460 lines
16 KiB
ReStructuredText
if
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--
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Conditionally execute a group of commands.
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Synopsis
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^^^^^^^^
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.. code-block:: cmake
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if(<condition>)
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<commands>
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elseif(<condition>) # optional block, can be repeated
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<commands>
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else() # optional block
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<commands>
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endif()
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Evaluates the ``condition`` argument of the ``if`` clause according to the
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`Condition syntax`_ described below. If the result is true, then the
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``commands`` in the ``if`` block are executed.
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Otherwise, optional ``elseif`` blocks are processed in the same way.
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Finally, if no ``condition`` is true, ``commands`` in the optional ``else``
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block are executed.
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Per legacy, the :command:`else` and :command:`endif` commands admit
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an optional ``<condition>`` argument.
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If used, it must be a verbatim
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repeat of the argument of the opening
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``if`` command.
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.. _`Condition Syntax`:
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Condition Syntax
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^^^^^^^^^^^^^^^^
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The following syntax applies to the ``condition`` argument of
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the ``if``, ``elseif`` and :command:`while` clauses.
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Compound conditions are evaluated in the following order of precedence:
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1. `Parentheses`_.
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2. Unary tests such as `EXISTS`_, `COMMAND`_, and `DEFINED`_.
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3. Binary tests such as `EQUAL`_, `LESS`_, `LESS_EQUAL`_, `GREATER`_,
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`GREATER_EQUAL`_, `STREQUAL`_, `STRLESS`_, `STRLESS_EQUAL`_,
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`STRGREATER`_, `STRGREATER_EQUAL`_, `VERSION_EQUAL`_, `VERSION_LESS`_,
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`VERSION_LESS_EQUAL`_, `VERSION_GREATER`_, `VERSION_GREATER_EQUAL`_,
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`PATH_EQUAL`_, and `MATCHES`_.
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4. Unary logical operator `NOT`_.
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5. Binary logical operators `AND`_ and `OR`_, from left to right,
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without any short-circuit.
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Basic Expressions
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"""""""""""""""""
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.. signature:: if(<constant>)
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:target: constant
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True if the constant is ``1``, ``ON``, ``YES``, ``TRUE``, ``Y``,
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or a non-zero number (including floating point numbers).
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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 (see `Variable Expansion`_
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further below) and one of the following two forms applies.
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.. signature:: if(<variable>)
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:target: variable
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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, including if the variable is undefined.
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Note that macro arguments are not variables.
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:ref:`Environment Variables <CMake Language Environment Variables>` also
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cannot be tested this way, e.g. ``if(ENV{some_var})`` will always evaluate
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to false.
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.. signature:: if(<string>)
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:target: string
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A quoted string always evaluates to false unless:
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* The string's value is one of the true constants, or
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* Policy :policy:`CMP0054` is not set to ``NEW`` and the string's value
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happens to be a variable name that is affected by :policy:`CMP0054`'s
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behavior.
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Logic Operators
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"""""""""""""""
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.. signature:: if(NOT <condition>)
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True if the condition is not true.
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.. signature:: if(<cond1> AND <cond2>)
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:target: AND
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True if both conditions would be considered true individually.
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.. signature:: if(<cond1> OR <cond2>)
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:target: OR
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True if either condition would be considered true individually.
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.. signature:: if((condition) AND (condition OR (condition)))
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:target: parentheses
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The conditions inside the parenthesis are evaluated first and then
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the remaining condition is evaluated as in the other examples.
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Where there are nested parenthesis the innermost are evaluated as part
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of evaluating the condition that contains them.
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Existence Checks
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""""""""""""""""
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.. signature:: 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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.. signature:: 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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.. signature:: if(TARGET <target-name>)
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True if the given name is an existing logical target name created
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by a call to the :command:`add_executable`, :command:`add_library`,
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or :command:`add_custom_target` command that has already been invoked
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(in any directory).
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.. signature:: if(TEST <test-name>)
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.. versionadded:: 3.3
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True if the given name is an existing test name created by the
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:command:`add_test` command.
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.. signature:: if(DEFINED <name>|CACHE{<name>}|ENV{<name>})
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True if a variable, cache variable or environment variable
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with given ``<name>`` is defined. The value of the variable
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does not matter. Note the following caveats:
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* Macro arguments are not variables.
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* It is not possible to test directly whether a `<name>` is a non-cache
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variable. The expression ``if(DEFINED someName)`` will evaluate to true
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if either a cache or non-cache variable ``someName`` exists. In
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comparison, the expression ``if(DEFINED CACHE{someName})`` will only
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evaluate to true if a cache variable ``someName`` exists. Both expressions
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need to be tested if you need to know whether a non-cache variable exists:
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``if(DEFINED someName AND NOT DEFINED CACHE{someName})``.
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.. versionadded:: 3.14
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Added support for ``CACHE{<name>}`` variables.
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.. signature:: if(<variable|string> IN_LIST <variable>)
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:target: IN_LIST
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.. versionadded:: 3.3
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True if the given element is contained in the named list variable.
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File Operations
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"""""""""""""""
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.. signature:: if(EXISTS <path-to-file-or-directory>)
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True if the named file or directory exists and is readable. Behavior
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is well-defined only for explicit full paths (a leading ``~/`` is not
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expanded as a home directory and is considered a relative path).
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Resolves symbolic links, i.e. if the named file or directory is a
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symbolic link, returns true if the target of the symbolic link exists.
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False if the given path is an empty string.
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.. signature:: if(<file1> IS_NEWER_THAN <file2>)
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:target: IS_NEWER_THAN
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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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.. signature:: if(IS_DIRECTORY <path>)
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True if ``path`` is a directory. Behavior is well-defined only
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for full paths.
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False if the given path is an empty string.
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.. signature:: if(IS_SYMLINK <path>)
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True if the given path is a symbolic link. Behavior is well-defined
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only for full paths.
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.. signature:: if(IS_ABSOLUTE <path>)
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True if the given path is an absolute path. Note the following special
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cases:
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* An empty ``path`` evaluates to false.
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* On Windows hosts, any ``path`` that begins with a drive letter and colon
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(e.g. ``C:``), a forward slash or a backslash will evaluate to true.
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This means a path like ``C:no\base\dir`` will evaluate to true, even
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though the non-drive part of the path is relative.
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* On non-Windows hosts, any ``path`` that begins with a tilde (``~``)
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evaluates to true.
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Comparisons
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"""""""""""
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.. signature:: if(<variable|string> MATCHES <regex>)
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:target: MATCHES
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True if the given string or variable's value matches the given regular
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expression. See :ref:`Regex Specification` for regex format.
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.. versionadded:: 3.9
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``()`` groups are captured in :variable:`CMAKE_MATCH_<n>` variables.
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.. signature:: if(<variable|string> LESS <variable|string>)
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:target: LESS
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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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.. signature:: if(<variable|string> GREATER <variable|string>)
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:target: GREATER
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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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.. signature:: if(<variable|string> EQUAL <variable|string>)
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:target: EQUAL
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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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.. signature:: if(<variable|string> LESS_EQUAL <variable|string>)
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:target: LESS_EQUAL
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.. versionadded:: 3.7
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True if the given string or variable's value is a valid number and less
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than or equal to that on the right.
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.. signature:: if(<variable|string> GREATER_EQUAL <variable|string>)
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:target: GREATER_EQUAL
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.. versionadded:: 3.7
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True if the given string or variable's value is a valid number and greater
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than or equal to that on the right.
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.. signature:: if(<variable|string> STRLESS <variable|string>)
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:target: STRLESS
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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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.. signature:: if(<variable|string> STRGREATER <variable|string>)
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:target: STRGREATER
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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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.. signature:: if(<variable|string> STREQUAL <variable|string>)
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:target: STREQUAL
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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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.. signature:: if(<variable|string> STRLESS_EQUAL <variable|string>)
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:target: STRLESS_EQUAL
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.. versionadded:: 3.7
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True if the given string or variable's value is lexicographically less
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than or equal to the string or variable on the right.
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.. signature:: if(<variable|string> STRGREATER_EQUAL <variable|string>)
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:target: STRGREATER_EQUAL
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.. versionadded:: 3.7
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True if the given string or variable's value is lexicographically greater
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than or equal to the string or variable on the right.
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Version Comparisons
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"""""""""""""""""""
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.. signature:: if(<variable|string> VERSION_LESS <variable|string>)
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:target: VERSION_LESS
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Component-wise integer version number comparison (version format is
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``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero).
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Any non-integer version component or non-integer trailing part of a version
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component effectively truncates the string at that point.
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.. signature:: if(<variable|string> VERSION_GREATER <variable|string>)
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:target: VERSION_GREATER
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Component-wise integer version number comparison (version format is
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``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero).
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Any non-integer version component or non-integer trailing part of a version
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component effectively truncates the string at that point.
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.. signature:: if(<variable|string> VERSION_EQUAL <variable|string>)
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:target: VERSION_EQUAL
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Component-wise integer version number comparison (version format is
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``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero).
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Any non-integer version component or non-integer trailing part of a version
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component effectively truncates the string at that point.
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.. signature:: if(<variable|string> VERSION_LESS_EQUAL <variable|string>)
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:target: VERSION_LESS_EQUAL
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.. versionadded:: 3.7
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Component-wise integer version number comparison (version format is
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``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero).
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Any non-integer version component or non-integer trailing part of a version
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component effectively truncates the string at that point.
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.. signature:: if(<variable|string> VERSION_GREATER_EQUAL <variable|string>)
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:target: VERSION_GREATER_EQUAL
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.. versionadded:: 3.7
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Component-wise integer version number comparison (version format is
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``major[.minor[.patch[.tweak]]]``, omitted components are treated as zero).
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Any non-integer version component or non-integer trailing part of a version
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component effectively truncates the string at that point.
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Path Comparisons
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""""""""""""""""
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.. signature:: if(<variable|string> PATH_EQUAL <variable|string>)
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:target: PATH_EQUAL
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.. versionadded:: 3.24
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Compares the two paths component-by-component. Only if every component of
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both paths match will the two paths compare equal. Multiple path separators
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are effectively collapsed into a single separator, but note that backslashes
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are not converted to forward slashes. No other
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:ref:`path normalization <Normalization>` is performed.
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Component-wise comparison is superior to string-based comparison due to the
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handling of multiple path separators. In the following example, the
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expression evaluates to true using ``PATH_EQUAL``, but false with
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``STREQUAL``:
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.. code-block:: cmake
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# comparison is TRUE
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if ("/a//b/c" PATH_EQUAL "/a/b/c")
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...
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endif()
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# comparison is FALSE
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if ("/a//b/c" STREQUAL "/a/b/c")
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...
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endif()
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See :ref:`cmake_path(COMPARE) <Path COMPARE>` for more details.
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Variable Expansion
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^^^^^^^^^^^^^^^^^^
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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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.. code-block:: cmake
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set(var1 OFF)
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set(var2 "var1")
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if(${var2})
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appears to the if command as
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.. code-block:: cmake
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if(var1)
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and is evaluated according to the ``if(<variable>)`` case documented
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above. The result is ``OFF`` which is false. However, if we remove the
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``${}`` from the example then the command sees
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.. code-block:: cmake
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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 condition syntax 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`_, `EQUAL`_,
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`LESS_EQUAL`_, and `GREATER_EQUAL`_, are independently tested to see if
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they are defined variables. If so, their defined values are used otherwise
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the original value is used.
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* Both left and right hand arguments to `STRLESS`_, `STRGREATER`_,
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`STREQUAL`_, `STRLESS_EQUAL`_, and `STRGREATER_EQUAL`_ are independently
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tested 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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* Both left and right hand arguments to `VERSION_LESS`_,
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`VERSION_GREATER`_, `VERSION_EQUAL`_, `VERSION_LESS_EQUAL`_, and
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`VERSION_GREATER_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 value
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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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.. versionchanged:: 3.1
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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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There is no automatic evaluation for environment or cache
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:ref:`Variable References`. Their values must be referenced as
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``$ENV{<name>}`` or ``$CACHE{<name>}`` wherever the above-documented
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condition syntax accepts ``<variable|string>``.
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See also
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^^^^^^^^
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* :command:`else`
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* :command:`elseif`
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* :command:`endif`
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