Set a normal, cache, or environment variable to a given value. See the cmake-language(7) variables documentation for the scopes and interaction of normal variables and cache entries.

Signatures of this command that specify a <value>... placeholder expect zero or more arguments. Multiple arguments will be joined as a ;-list to form the actual variable value to be set. Zero arguments will cause normal variables to be unset. See the unset() command to unset variables explicitly.

Set Normal Variable

set(<variable> <value>... [PARENT_SCOPE])

Set the given <variable> in the current function or directory scope.

If the PARENT_SCOPE option is given the variable will be set in the scope above the current scope. Each new directory or function creates a new scope. This command will set the value of a variable into the parent directory or calling function (whichever is applicable to the case at hand). The previous state of the variable’s value stays the same in the current scope (e.g., if it was undefined before, it is still undefined and if it had a value, it is still that value).

Set Cache Entry

set(<variable> <value>... CACHE <type> <docstring> [FORCE])

Set the given cache <variable> (cache entry). Since cache entries are meant to provide user-settable values this does not overwrite existing cache entries by default. Use the FORCE option to overwrite existing entries.

The <type> must be specified as one of:


Boolean ON/OFF value. cmake-gui(1) offers a checkbox.


Path to a file on disk. cmake-gui(1) offers a file dialog.


Path to a directory on disk. cmake-gui(1) offers a file dialog.


A line of text. cmake-gui(1) offers a text field or a drop-down selection if the STRINGS cache entry property is set.


A line of text. cmake-gui(1) does not show internal entries. They may be used to store variables persistently across runs. Use of this type implies FORCE.

The <docstring> must be specified as a line of text providing a quick summary of the option for presentation to cmake-gui(1) users.

If the cache entry does not exist prior to the call or the FORCE option is given then the cache entry will be set to the given value. Furthermore, any normal variable binding in the current scope will be removed to expose the newly cached value to any immediately following evaluation.

It is possible for the cache entry to exist prior to the call but have no type set if it was created on the cmake(1) command line by a user through the -D<var>=<value> option without specifying a type. In this case the set command will add the type. Furthermore, if the <type> is PATH or FILEPATH and the <value> provided on the command line is a relative path, then the set command will treat the path as relative to the current working directory and convert it to an absolute path.

Set Environment Variable

set(ENV{<variable>} <value>...)

Set the current process environment <variable> to the given value.