Conditionally execute a group of commands.
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.
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: 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
. Then the boolean operators in the order NOT
, AND
, and finally OR
.
Possible conditions are:
if(<constant>)
1
, ON
, YES
, TRUE
, Y
, or a non-zero number. 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 and the following signature is used.if(<variable|string>)
if(NOT <condition>)
if(<cond1> AND <cond2>)
if(<cond1> OR <cond2>)
if(COMMAND command-name)
if(POLICY policy-id)
CMP<NNNN>
).if(TARGET target-name)
add_executable()
, add_library()
, or add_custom_target()
command that has already been invoked (in any directory).if(TEST test-name)
add_test()
command.if(EXISTS path-to-file-or-directory)
if(file1 IS_NEWER_THAN file2)
file1
is newer than file2
or if one of the two files doesn’t exist. Behavior is well-defined only for full paths. If the file time stamps are exactly the same, an IS_NEWER_THAN
comparison returns true, so that any dependent build operations will occur in the event of a tie. This includes the case of passing the same file name for both file1 and file2.if(IS_DIRECTORY path-to-directory)
if(IS_SYMLINK file-name)
if(IS_ABSOLUTE path)
if(<variable|string> MATCHES regex)
()
groups are captured in CMAKE_MATCH_<n>
variables.if(<variable|string> LESS <variable|string>)
if(<variable|string> GREATER <variable|string>)
if(<variable|string> EQUAL <variable|string>)
if(<variable|string> LESS_EQUAL <variable|string>)
if(<variable|string> GREATER_EQUAL <variable|string>)
if(<variable|string> STRLESS <variable|string>)
if(<variable|string> STRGREATER <variable|string>)
if(<variable|string> STREQUAL <variable|string>)
if(<variable|string> STRLESS_EQUAL <variable|string>)
if(<variable|string> STRGREATER_EQUAL <variable|string>)
if(<variable|string> VERSION_LESS <variable|string>)
major[.minor[.patch[.tweak]]]
, omitted components are treated as zero). Any non-integer version component or non-integer trailing part of a version component effectively truncates the string at that point.if(<variable|string> VERSION_GREATER <variable|string>)
major[.minor[.patch[.tweak]]]
, omitted components are treated as zero). Any non-integer version component or non-integer trailing part of a version component effectively truncates the string at that point.if(<variable|string> VERSION_EQUAL <variable|string>)
major[.minor[.patch[.tweak]]]
, omitted components are treated as zero). Any non-integer version component or non-integer trailing part of a version component effectively truncates the string at that point.if(<variable|string> VERSION_LESS_EQUAL <variable|string>)
major[.minor[.patch[.tweak]]]
, omitted components are treated as zero). Any non-integer version component or non-integer trailing part of a version component effectively truncates the string at that point.if(<variable|string> VERSION_GREATER_EQUAL <variable|string>)
major[.minor[.patch[.tweak]]]
, omitted components are treated as zero). Any non-integer version component or non-integer trailing part of a version component effectively truncates the string at that point.if(<variable|string> IN_LIST <variable>)
if(DEFINED <name>|CACHE{<name>}|ENV{<name>})
<name>
is defined. The value of the variable does not matter. Note that macro arguments are not variables.if((condition) AND (condition OR (condition)))
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 ${}
applies before the if command even receives the arguments. Therefore code like
set(var1 OFF) set(var2 "var1") if(${var2})
appears to the if command as
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
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 condition syntax accepts <variable|string>
:
MATCHES
is first checked to see if it is a defined variable, if so the variable’s value is used, otherwise the original value is used.MATCHES
is missing it returns false without errorLESS
, GREATER
, EQUAL
, LESS_EQUAL
, and GREATER_EQUAL
, are independently tested to see if they are defined variables, if so their defined values are used otherwise the original value is used.STRLESS
, STRGREATER
, STREQUAL
, STRLESS_EQUAL
, and STRGREATER_EQUAL
are independently tested to see if they are defined variables, if so their defined values are used otherwise the original value is used.VERSION_LESS
, VERSION_GREATER
, VERSION_EQUAL
, VERSION_LESS_EQUAL
, and VERSION_GREATER_EQUAL
are independently tested to see if they are defined variables, if so their defined values are used otherwise the original value is used.NOT
is tested to see if it is a boolean constant, if so the value is used, otherwise it is assumed to be a variable and it is dereferenced.AND
and OR
are independently tested to see if they are boolean constants, if so they are used as such, otherwise they are assumed to be variables and are dereferenced.To prevent ambiguity, potential variable or keyword names can be specified in a Quoted Argument or a Bracket Argument. A quoted or bracketed variable or keyword will be interpreted as a string and not dereferenced or interpreted. See policy CMP0054
.
There is no automatic evaluation for environment or cache Variable References. Their values must be referenced as $ENV{<name>}
or $CACHE{<name>}
wherever the above-documented condition syntax accepts <variable|string>
.
© 2000–2019 Kitware, Inc. and Contributors
Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.15/command/if.html