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Diffstat (limited to 'Help/command/if.rst')
| -rw-r--r-- | Help/command/if.rst | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/Help/command/if.rst b/Help/command/if.rst index b4b4897..5dba13e 100644 --- a/Help/command/if.rst +++ b/Help/command/if.rst @@ -56,15 +56,24 @@ Basic Expressions ``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. + constants, it is treated as a variable or string (see `Variable Expansion`_ + further below) and one of the following two forms applies. -``if(<variable|string>)`` +``if(<variable>)`` True if given a variable that is defined to a value that is not a false - constant. False otherwise. Note that macro arguments are not variables. + constant. False otherwise, including if the variable is undefined. + Note that macro arguments are not variables. Environment variables also cannot be tested this way, e.g. ``if(ENV{some_var})`` will always evaluate to false. +``if(<string>)`` + A quoted string always evaluates to false unless: + + * The string's value is one of the true constants, or + * Policy :policy:`CMP0054` is not set to ``NEW`` and the string's value + happens to be a variable name that is affected by :policy:`CMP0054`'s + behavior. + Logic Operators """"""""""""""" |