# Copy file on every cmake command

**URL:** <https://discourse.cmake.org/t/copy-file-on-every-cmake-command/4561>\
**Category:** Code\
**Created:** [November 27, 2021, 9:42am UTC](https://discourse.cmake.org/t/copy-file-on-every-cmake-command/4561 "2021-11-27T09:42:14Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Leon0402](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/l/ccd318/32.png) [@Leon0402](https://discourse.cmake.org/u/Leon0402)\
**Post date:** [November 27, 2021, 9:42am UTC](https://discourse.cmake.org/t/copy-file-on-every-cmake-command/4561/1 "2021-11-27T09:42:14Z")

</div>

I use VS Code together with compile\_commands.json and my extension / language server needs to know where the compile\_commands.json lives.

The problem is that I use multiple build directories / presets and therefore the path to compile\_commands.json is not static.

My idea is basically to always copy the “active” compile\_commands.json in the root folder, so the path is always static.

I do want the current active compile\_commands.json as fast as possible, therefore it should be copied on as much cmake commands as possible.

`cmake -B build` → Should copy the file  
`cmake --build build` → Should copy the file  
`cmake --build build --target target` → Should copy the file  
`ctest ...` → Ideally should copy the file as well

I know of some ways to copy files as part of a target or post target.

But I don’t know an easy way. I don’t want to specify a post build for every target I have (What’s about targets like install, which are generated automatically …).

So what could be the best and easiest way to achieve that?

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<div class="post-metadata">

**Author:** ![ben.boeckel](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/b/ea5d25/32.png) [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)\
**Post date:** [November 28, 2021, 12:29am UTC](https://discourse.cmake.org/t/copy-file-on-every-cmake-command/4561/2 "2021-11-28T00:29:27Z")

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You can sort of make this work by doing:

```cmake
set(output "${CMAKE_SOURCE_DIR}/compile_commands.json")
if (EXISTS "${output}")
  # Add a dependency on the file to CMake so that if it changes, CMake reruns (which should happen on any non-`/fast` target.
  file(READ "${output}" ignored)
  unset(ignored) # Drop the memory
endif ()
set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
# This *might* work. I don't know if `compile_commands.json` is guaranteed to be written before `file(GENERATE)` runs. If not…I don't know what else might run this late.
file(GENERATE
  INPUT "${CMAKE_BINARY_DIR}/compile_commands.json"
  OUTPUT "${output}")

```

This almost certainly makes some odd behaviors come up with CMake rerunning “unnecessarily” and as such I’d recommend guarding this behind an “I’m a developer” flag of some kind.