Passing env var between steps fails on Windows runners if var written to ${{ github.env }}

[MarkCallow]

Why are you starting this discussion?

Bug

What GitHub Actions topic or product is this about?

Actions Runner

Discussion Details

If I have the following in my workflow

- name: Prepare version number for artifact
  id: libktx-version
  shell: bash
  run: echo KTX_VERSION=$(grep -A 1 -m 1 "Code version" lib/src/version.h | tail -n 1) >> $GITHUB_ENV

- name: Upload artifact libktx
  uses: actions/upload-artifact@v4
    with:
      name: libktx-${{ env.KTX_VERSION }}
      path: ${{env.BUILD_DIR}}/Release/*ktx*

it works on Linux, macOS and Windows runners. If I change the run in the first step to

  run: echo KTX_VERSION=$(grep -A 1 -m 1 "Code version" lib/src/version.h | tail -n 1) >> ${{ github.env }}

then on Windows runners the second step does not see KTX_VERSION so the artifact name is just libktx-. It works fine on Linux and macOS runners.

It looks like a bug to me but I have no idea the proper place to file an issue.

[John0n1]

Use $GITHUB_ENV, not ${{ github.env }}, when you’re in a bash shell on Windows. ${{ github.env }} expands to a native Windows path like D:\a... which MSYS/MinGW bash doesn’t understand properly, so the redirect silently fails and the var never gets written (hence libktx-). Cross‑platform safe example:

• name: Prepare version number for artifact
  id: libktx-version
  shell: bash
  run: |
  echo "KTX_VERSION=$(grep -A1 -m1 'Code version' lib/src/version.h | tail -n 1)" >> "$GITHUB_ENV"

If you really want to use ${{ github.env }}, switch the step’s shell on Windows to pwsh or cmd. Otherwise just stick with $GITHUB_ENV.

If you think it’s a runner bug, file it here: https://github.com/actions/runner/issues

Hope that helps!

[MarkCallow]

The explanation sounds plausible except that when debugging the problem the run at one point looked like this

run: |
  echo KTX_VERSION=$(grep -A 1 -m 1 "Code version" lib/src/version.h | tail -n 1) >> ${{ github.env }}
  grep KTX_VERSION ${{ github.env }}

which displayed the expected KTX_VERSION=<version> output from grep in the log. So the value was getting written somewhere. It seems bash must have interpreted the Windows path in some way but in a different way to the following upload step.

I have since encountered another oddity with Windows runners and bash. I have another step

- name: Check output directory content
  run: scripts/check_lib_build_output.sh ${{ env.BUILD_DIR }}/${{ matrix.config }}

which worked but I thought I should explicitly name the shell it needs so I changed it to

- name: Check output directory content
  shell: bash
  run: scripts/check_lib_build_output.sh ${{ env.BUILD_DIR }}/${{ matrix.config }}

After that it gets an empty string for ${{ matrix.config }}. Very strange.

[John0n1]

Yeah, that’s odd. Seeing the line just means bash wrote somewhere, it doesn't prove the runner loaded it.. The matrix value dropping when you set Bash points more to scope (composite/reusable workflow) or a subtle mismatch than to the shell itself..
Could you share the strategy.matrix section (showing the key you expect) and whether that step sits inside a composite action or a called/reusable workflow?

Tiny debug:

- name: Debug env ingestion
  shell: bash
  run: |
    echo "GITHUB_ENV=$GITHUB_ENV"
    echo "Content of env file:"
    cat "$GITHUB_ENV"

- name: Check matrix value
  run: echo "matrix.config='${{ matrix.config }}'"

We can try to zero in. But again, it's indeed odd. Happy to dig further!