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Diffstat (limited to 'Help/command/if.rst')
| -rw-r--r-- | Help/command/if.rst | 120 |
1 files changed, 71 insertions, 49 deletions
diff --git a/Help/command/if.rst b/Help/command/if.rst index 5294ce8..a682c83 100644 --- a/Help/command/if.rst +++ b/Help/command/if.rst @@ -3,41 +3,49 @@ if Conditionally execute a group of commands. +Synopsis +^^^^^^^^ + .. code-block:: cmake - if(expression) - # then section. - COMMAND1(ARGS ...) - COMMAND2(ARGS ...) - #... - elseif(expression2) - # elseif section. - COMMAND1(ARGS ...) - COMMAND2(ARGS ...) - #... - else(expression) - # else section. - COMMAND1(ARGS ...) - COMMAND2(ARGS ...) - #... - endif(expression) - -Evaluates the given expression. If the result is true, the commands -in the THEN section are invoked. Otherwise, the commands in the else -section are invoked. The elseif and else sections are optional. You -may have multiple elseif clauses. Note that the expression in the -else and endif clause is optional. Long expressions can be used and -there is a traditional order of precedence. Parenthetical expressions -are evaluated first followed by unary tests such as ``EXISTS``, -``COMMAND``, and ``DEFINED``. Then any binary tests such as + 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:`elseif` commands admit +an optional ``<condition>`` argument. +If used, it must be a verbatim +repeat of the argument of the opening +``if`` command. + +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`` will be evaluated. Then boolean ``NOT`` operators and -finally boolean ``AND`` and then ``OR`` operators will be evaluated. +and ``MATCHES``. Then the boolean operators in the order ``NOT``, ``AND``, +and finally ``OR``. -Possible expressions are: +Possible conditions are: ``if(<constant>)`` True if the constant is ``1``, ``ON``, ``YES``, ``TRUE``, ``Y``, @@ -52,14 +60,14 @@ Possible expressions are: 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 <expression>)`` - True if the expression is not true. +``if(NOT <condition>)`` + True if the condition is not true. -``if(<expr1> AND <expr2>)`` - True if both expressions would be considered true individually. +``if(<cond1> AND <cond2>)`` + True if both conditions would be considered true individually. -``if(<expr1> OR <expr2>)`` - True if either expression 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 @@ -103,7 +111,7 @@ Possible expressions are: ``if(<variable|string> MATCHES regex)`` True if the given string or variable's value matches the given regular - expression. See :ref:`Regex Specification` for regex format. + condition. See :ref:`Regex Specification` for regex format. ``()`` groups are captured in :variable:`CMAKE_MATCH_<n>` variables. ``if(<variable|string> LESS <variable|string>)`` @@ -179,42 +187,51 @@ Possible expressions are: ``if(<variable|string> IN_LIST <variable>)`` True if the given element is contained in the named list variable. -``if(DEFINED <variable>)`` - True if the given variable is defined. It does not matter if the - variable is true or false just if it has been set. (Note macro - arguments are not variables.) +``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((expression) AND (expression OR (expression)))`` - The expressions inside the parenthesis are evaluated first and then - the remaining expression is evaluated as in the previous examples. +``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 expression that contains them. + 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:: +command even receives the arguments. Therefore code like + +.. code-block:: cmake set(var1 OFF) set(var2 "var1") if(${var2}) -appears to the if command as:: +appears to the if command as - if(var1) +.. code-block:: cmake + + if(var1) and is evaluated according to the ``if(<variable>)`` case documented above. The result is ``OFF`` which is false. However, if we remove the -``${}`` from the example then the command sees:: +``${}`` from the example then the command sees + +.. code-block:: cmake - if(var2) + if(var2) which is true because ``var2`` is defined to "var1" which is not a false constant. Automatic evaluation applies in the other cases whenever the -above-documented signature accepts ``<variable|string>``: +above-documented condition syntax accepts ``<variable|string>``: * The left hand argument to ``MATCHES`` is first checked to see if it is a defined variable, if so the variable's value is used, otherwise the @@ -252,3 +269,8 @@ specified in a :ref:`Quoted Argument` or a :ref:`Bracket Argument`. A quoted or bracketed variable or keyword will be interpreted as a string and not dereferenced or interpreted. See policy :policy:`CMP0054`. + +There is no automatic evaluation for environment or cache +:ref:`Variable References`. Their values must be referenced as +``$ENV{<name>}`` or ``$CACHE{<name>}`` wherever the above-documented +condition syntax accepts ``<variable|string>``. |