# How to tell execute\_process to preserve ansi colors in its output?

**URL:** https://discourse.cmake.org/t/how-to-tell-execute-process-to-preserve-ansi-colors-in-its-output/15296
**Category:** Code
**Created:** [November 12, 2025, 12:06pm UTC](https://discourse.cmake.org/t/how-to-tell-execute-process-to-preserve-ansi-colors-in-its-output/15296 "2025-11-12T12:06:43Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![alcroito](https://discourse.cmake.org/user_avatar/discourse.cmake.org/alcroito/32/186_2.png) [@alcroito](https://discourse.cmake.org/u/alcroito)
#### Post date: [November 12, 2025, 12:06pm UTC](https://discourse.cmake.org/t/how-to-tell-execute-process-to-preserve-ansi-colors-in-its-output/15296/1 "2025-11-12T12:06:43Z")

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Sample project

```cmake
cmake_minimum_required(VERSION 3.16)

if(NOT CMAKE_SCRIPT_MODE_FILE)
    project(proj LANGUAGES NONE)
endif()

message(WARNING "This is a warning")

if(NOT NESTED_CALL)
    execute_process(
        COMMAND
            "${CMAKE_COMMAND}"
            -DNESTED_CALL=1
            -P
            "${CMAKE_CURRENT_LIST_FILE}"
    )
endif()

```

When I configure the sample project with a recent `cmake` (v4.1) on macOS in the iTerm2 terminal, I get

```auto
CMake Warning at CMakeLists.txt:7 (message):
  This is a warning <--------------------- this shows as yellow text

CMake Warning at /Users/alex/Dev/projects/cmake/general/nested_cmake_ansi_colors/CMakeLists.txt:7 (message):
  This is a warning <--------------------- this shows as white text

```

So the second message gets its color lost.

I can force the color to show if I set the `export CLICOLOR_FORCE=1` env variable before the `execute_process` call, but I can’t do this universally because I don’t know if the outer cmake call is connected to a terminal / tty and whether the terminal supports colors.

Is this a bug or a missing feature in `execute_process`?

Shouldn’t `execute_process` treat the stdout as just another piped output to the cmake’s stdout, because it doesn’t have the `OUTPUT_FILE` / `ERROR_FILE` options set to redirect to a different file?

---

<div class="post-metadata">

### Author: ![brad.king](https://discourse.cmake.org/user_avatar/discourse.cmake.org/brad.king/32/11_2.png) [@brad.king](https://discourse.cmake.org/u/brad.king)
#### Post date: [November 12, 2025, 3:00pm UTC](https://discourse.cmake.org/t/how-to-tell-execute-process-to-preserve-ansi-colors-in-its-output/15296/2 "2025-11-12T15:00:08Z")

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`execute_process` by default captures the output so that it can be printed wherever CMake’s output is going, which might be `cmake-gui` or `ccmake` display buffers instead of a real terminal. One could add an option to pass through the real pipes, at least when called from a command-line tool like `cmake`.

---

<div class="post-metadata">

### Author: ![adi](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/a/4da419/32.png) [@adi](https://discourse.cmake.org/u/adi)
#### Post date: [October 16, 2026, 8:44am UTC](https://discourse.cmake.org/t/how-to-tell-execute-process-to-preserve-ansi-colors-in-its-output/15296/3 "2026-10-16T08:44:14Z")

</div>

I came here after I tried to implement colors in Zephyr’s sysbuild. Zephyr’s sysbuild does run CMake inside a CMake `execute_process`. See [Zephyr Bug 106182](https://github.com/zephyrproject-rtos/zephyr/issues/106182) for details. I tried a workaround with setting `OUTPUT_FILE` and `ERROR_FILE` to `/dev/stdout` and `/dev/stderr`, respectively. But that only works on Unix and has other issues.

@brad.king your answer explains the reason for that implementation detail, thanks. CMake would have to open a pseudoterminal for the process started by `execute_process`, in order to make it believe it runs in a terminal and for CMake still being able to capture the output.

Are there simpler solutions to implement CMake printing colors when started by CMake, but only when the outer CMake is run in a terminal?