Conditionally execute a group of commands.
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 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.
Possible expressions 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 <expression>)
if(<expr1> AND <expr2>)
if(<expr1> OR <expr2>)
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]]]
).if(<variable|string> VERSION_GREATER <variable|string>)
major[.minor[.patch[.tweak]]]
).if(<variable|string> VERSION_EQUAL <variable|string>)
major[.minor[.patch[.tweak]]]
).if(<variable|string> VERSION_LESS_EQUAL <variable|string>)
major[.minor[.patch[.tweak]]]
).if(<variable|string> VERSION_GREATER_EQUAL <variable|string>)
major[.minor[.patch[.tweak]]]
).if(<variable|string> IN_LIST <variable>)
if(DEFINED <variable>)
if((expression) AND (expression OR (expression)))
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 signature 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
.
© 2000–2018 Kitware, Inc. and Contributors
Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.12/command/if.html