# Example: GNU Patch from CMake
**URL:** https://discourse.cmake.org/t/example-gnu-patch-from-cmake/4492
**Category:** Code
**Created:** [November 16, 2021, 5:04pm UTC](https://discourse.cmake.org/t/example-gnu-patch-from-cmake/4492 "2021-11-16T17:04:10Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@scivision](https://discourse.cmake.org/u/scivision)
#### Post date: [November 16, 2021, 5:04pm UTC](https://discourse.cmake.org/t/example-gnu-patch-from-cmake/4492/1 "2021-11-16T17:04:10Z")
To patch files in one’s own project, or when using other projects via FetchContent etc., it’s possible to patch source/header/etc. using GNU Patch and add\_custom\_command() with the benefit of CMake canonical approach (triggers only if source changes).
I have seen requests for this but didn’t find a cross-platform solution (Linux, MacOS, Windows) so I made an example. It requires that GNU Patch “patch” is available, which is usually is. On Windows, MSYS2 or WSL are used to get patch executable.
> **[GitHub - scivision/cmake-patch-file: Use GNU Patch from CMake to patch...](https://github.com/scivision/cmake-patch-file)**
>
> Use GNU Patch from CMake to patch source/headers/etc. - GitHub - scivision/cmake-patch-file: Use GNU Patch from CMake to patch source/headers/etc.
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### Author:  [@bertulli](https://discourse.cmake.org/u/bertulli)
#### Post date: [August 1, 2025, 3:09pm UTC](https://discourse.cmake.org/t/example-gnu-patch-from-cmake/4492/2 "2025-08-01T15:09:27Z")
thanks, this really helped me! a thing though: if the file to patch is inside a git submodule, copying it in the build directory doesn’t make it build. i tested and overwriting the file in the source directory works, but runs only if it is a clean build i think, because the timestamp of the modified file will always be newer if you change it. also, i added a add\_custom\_target with the specified dependency to make the build system know it has to build it before the using project