if¶

Conditionally execute a group of commands.

Synopsis¶

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 else() and 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¶

The following syntax applies to the condition argument of the if, elseif and while() clauses.

Compound conditions are evaluated in the following order of precedence:

Parentheses.
Unary tests such as EXISTS, COMMAND, and DEFINED.
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, PATH_EQUAL, and MATCHES.
Unary logical operator NOT.
Binary logical operators AND and OR, from left to right, without any short-circuit.

Basic Expressions¶

if(<constant>)¶: True if the constant is 1, ON, YES, TRUE, Y, or a non-zero number (including floating point numbers). 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 (see Variable Expansion further below) and one of the following two forms applies.

if(<variable>)¶: True if given a variable that is defined to a value that is not a false 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 CMP0054 is not set to NEW and the string's value happens to be a variable name that is affected by CMP0054's behavior.

Logic Operators¶

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((condition) AND (condition OR (condition)))¶: The conditions inside the parenthesis are evaluated first and then the remaining condition is evaluated as in the other examples. Where there are nested parenthesis the innermost are evaluated as part of evaluating the condition that contains them.

Existence Checks¶

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 add_executable(), add_library(), or add_custom_target() command that has already been invoked (in any directory).

if(TEST <test-name>)¶: New in version 3.3.

True if the given name is an existing test name created by the add_test() command.

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 the following caveats:

Macro arguments are not variables.

It is not possible to test directly whether a <name> is a non-cache variable. The expression if(DEFINED someName) will evaluate to true if either a cache or non-cache variable someName exists. In comparison, the expression if(DEFINED CACHE{someName}) will only evaluate to true if a cache variable someName exists. Both expressions need to be tested if you need to know whether a non-cache variable exists: if(DEFINED someName AND NOT DEFINED CACHE{someName}).

New in version 3.14: Added support for CACHE{<name>} variables.

if(<variable|string> IN_LIST <variable>)¶: New in version 3.3.

True if the given element is contained in the named list variable.

File Operations¶

if(EXISTS <path-to-file-or-directory>)¶

True if the named file or directory exists and is readable. Behavior is well-defined only for explicit full paths (a leading ~/ is not expanded as a home directory and is considered a relative path). 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.