# configure_file

Copy a file to another location and modify its contents.

    configure_file(<input> <output>
                   [NO_SOURCE_PERMISSIONS | USE_SOURCE_PERMISSIONS |
                    FILE_PERMISSIONS <permissions>...]
                   [COPYONLY] [ESCAPE_QUOTES] [@ONLY]
                   [NEWLINE_STYLE [UNIX|DOS|WIN32|LF|CRLF] ])

Copies an `<input>` file to an `<output>` file while performing transformations of the input file content.

If the input file is modified the build system will re-run CMake to re-configure the file and generate the build system again. The generated file is modified and its timestamp updated on subsequent cmake runs only if its content is changed.

## Options

The options are:

`<input>`

  Path to the input file. A relative path is treated with respect to the value of `CMAKE_CURRENT_SOURCE_DIR`. The input path must be a file, not a directory.

`<output>`

  Path to the output file or directory. A relative path is treated with respect to the value of `CMAKE_CURRENT_BINARY_DIR`. If the path names an existing directory the output file is placed in that directory with the same file name as the input file. If the path contains non-existent directories, they are created.

`NO_SOURCE_PERMISSIONS`

  Added in version 3.19.

  Do not transfer the permissions of the input file to the output file. The copied file permissions default to the standard 644 value (-rw-r--r--).

`USE_SOURCE_PERMISSIONS`

  Added in version 3.20.

  Transfer the permissions of the input file to the output file. This is already the default behavior if none of the three permissions-related keywords are given (`NO_SOURCE_PERMISSIONS`, `USE_SOURCE_PERMISSIONS` or `FILE_PERMISSIONS`). The `USE_SOURCE_PERMISSIONS` keyword mostly serves as a way of making the intended behavior clearer at the call site.

`FILE_PERMISSIONS <permissions>...`

  Added in version 3.20.

  Ignore the input file's permissions and use the specified `<permissions>` for the output file instead.

`COPYONLY`

  Copy the file without replacing any variable references or other content. This option may not be used with `NEWLINE_STYLE`.

`ESCAPE_QUOTES`

  Escape any substituted quotes with backslashes (C-style).

`@ONLY`

  Restrict variable replacement to references of the form `@VAR@`. This is useful for configuring scripts that use `${VAR}` syntax.

`NEWLINE_STYLE <style>`

  Specify the newline style for the output file. Specify `UNIX` or `LF` for `\n` newlines, or specify `DOS`, `WIN32`, or `CRLF` for `\r\n` newlines. This option may not be used with `COPYONLY`.

## Transformations

Variables referenced in the input file content as `@VAR@`, `${VAR}`, `$CACHE{VAR}`, and environment variables referenced as `$ENV{VAR}`, will each be replaced with the current value of the variable, or the empty string if the variable is not defined. Furthermore, input lines of the form

    #cmakedefine VAR ...

will be replaced with either

    #define VAR ...

or

    /* #undef VAR */

depending on whether `VAR` is set in CMake to any value not considered a false constant by the `if()` command. The "..." content on the line after the variable name, if any, is processed as above.

Unlike lines of the form `#cmakedefine VAR ...`, in lines of the form `#cmakedefine01 VAR`, `VAR` itself will expand to `VAR 0` or `VAR 1` rather than being assigned the value `...`. Therefore, input lines of the form

    #cmakedefine01 VAR

will be replaced with either

    #define VAR 0

or

    #define VAR 1

Input lines of the form `#cmakedefine01 VAR ...` will expand as `#cmakedefine01 VAR ... 0` or `#cmakedefine01 VAR ... 1`, which may lead to undefined behavior.

Added in version 3.10: The result lines (with the exception of the `#undef` comments) can be indented using spaces and/or tabs between the `#` character and the `cmakedefine` or `cmakedefine01` words. This whitespace indentation will be preserved in the output lines:

    #  cmakedefine VAR
    #  cmakedefine01 VAR

will be replaced, if `VAR` is defined, with

    #  define VAR
    #  define VAR 1

## Example

Consider a source tree containing a `foo.h.in` file:

    #cmakedefine FOO_ENABLE
    #cmakedefine FOO_STRING "@FOO_STRING@"

An adjacent `CMakeLists.txt` may use `configure_file` to configure the header:

    option(FOO_ENABLE "Enable Foo" ON)
    if(FOO_ENABLE)
      set(FOO_STRING "foo")
    endif()
    configure_file(foo.h.in foo.h @ONLY)

This creates a `foo.h` in the build directory corresponding to this source directory. If the `FOO_ENABLE` option is on, the configured file will contain:

    #define FOO_ENABLE
    #define FOO_STRING "foo"

Otherwise it will contain:

    /* #undef FOO_ENABLE */
    /* #undef FOO_STRING */

One may then use the `target_include_directories()` command to specify the output directory as an include directory:

    target_include_directories(<target> [SYSTEM] <INTERFACE|PUBLIC|PRIVATE> "${CMAKE_CURRENT_BINARY_DIR}")

so that sources may include the header as `#include <foo.h>`.

## See Also

- `file(GENERATE)`