How to reference context values in GitHub Actions expression syntax?

Question

I want to set an environment variable in the env: section of a GitHub Action and make use of the Contexts and expression syntax for GitHub Actions. I tried this:

jobs:
  build:
    runs-on: ubuntu-latest

    env:
      MYVAR: ${{ format('{0}:{1}', ${{ env.PATH }}, ${{ env.HOME }} ) }}

    steps:
    - name: Check environment
      run: echo $MYVAR

This results in the error message:

### ERRORED 10:45:52Z

- Your workflow file was invalid: The pipeline is not valid. .github/workflows/main.yml (Line: 10, Col: 14): Unexpected symbol: '${{'. Located at position 19 within expression: format('{0}:{1}', ${{ env.PATH

This syntax:

    env:
      MYVAR: ${{ format('{0}:{1}', {{ env.PATH }}, {{ env.HOME }} ) }}

results in error:

### ERRORED 13:14:18Z

- Your workflow file was invalid: The pipeline is not valid. .github/workflows/main.yml (Line: 10, Col: 14): Unexpected symbol: '{{'. Located at position 19 within expression: format('{0}:{1}', {{ env.PATH

and:

    env:
      MYVAR: ${{ format('{0}:{1}', env.PATH, env.HOME ) }}

results in error:

### ERRORED 13:16:12Z

- Your workflow file was invalid: The pipeline is not valid. .github/workflows/main.yml (Line: 10, Col: 14): Unrecognized named-value: 'env'. Located at position 19 within expression: format('{0}:{1}', env.PATH, env.HOME )

I'm aware of the solutions in How do i set an env var with a bash expression in GitHub Actions? and Github Actions, how to share a calculated value between job steps? for setting environment variables, but I would like to understand the expression syntax.

Why have you put `${{` inside `${{`? Also note that [`format`](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/contexts-and-expression-syntax-for-github-actions#format) takes 0-based indices. — jonrsharpe, Jan 19 '20 at 11:56
Because it says under https://help.github.com/en/actions/automating-your-workflow-with-github-actions/contexts-and-expression-syntax-for-github-actions#contexts : "Contexts are a way to access information about workflow runs, runner environments, jobs, and steps. Contexts use the expression syntax. {{ }}" — stm, Jan 19 '20 at 11:59
None of the examples on that page, including those using contexts, have more than one `${{`. I'd guess you want `${{ format('{0}:{1}', env.PATH env.HOME) }}`. — jonrsharpe, Jan 19 '20 at 12:01
Thanks for the information about the 0-based index, I missed that. But it doesn't help. With the syntax you proposed I get: "- Your workflow file was invalid: The pipeline is not valid. .github/workflows/main.yml (Line: 10, Col: 14): Unrecognized named-value: 'env'. Located at position 19 within expression: format('{0}:{1}', env.PATH, env.HOME )" — stm, Jan 19 '20 at 12:05
I had alread tried the syntax that you proposed. This was the third try in the original question. Note that I fixed the indices in the format string now. — stm, Jan 19 '20 at 12:09
But that's *not* a similar error message. Sure the start is the same, but the *reason* is different. `Unexpected symbol: '${{'.` is not the same as `Unrecognized named-value: 'env'.` I would recommend researching those specific parts of the error, and including that in your question to make it more searchable. — jonrsharpe, Jan 19 '20 at 12:11
For example, the specific error around named-value led me to https://github.community/t5/GitHub-Actions/How-to-use-env-context/td-p/38951 - *"You cannot use env context in the value of a workflow environment variable."* — jonrsharpe, Jan 19 '20 at 12:15

score 4 · Answer 1 · answered Apr 20 '21 at 00:48

At the start of a workflow, the env context doesn't exist yet. This is why you get an error. Moreover, the first step in every job sees an empty env context, so even if env existed, the result of printing MYVAR would have been just :.

I came to the above conclusions from running some experiments.

env:
  MYVAR: ${{ format('{0}:{1}', env.PATH, env.HOME) }}

The last syntax you used is the correct form, but because the env context doesn't exist yet, the workflow fails to run.

To prove to yourself that the env context is in fact empty at the first step, try the following job:

jobs
  env-dump-context:
    runs-on: ubuntu-latest
    steps:
      - run: echo env is: ${{ toJSON(env) }}

With that being said, it is still possible to what you need:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - run: printf "MYVAR=${PATH}:${HOME}" | tee --append "$GITHUB_ENV"
      - name: Check environment
        run: echo ${{env.MYVAR}}

score 3 · Answer 2 · answered Jan 19 '20 at 18:34

3

As @jonrsharpe pointed out, it is not possible to use the env context in the value of a workflow environment variable. This was discussed here:

https://github.community/t5/GitHub-Actions/How-to-use-env-context/td-p/38951

answered Jan 19 '20 at 18:34

stm

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It looks like it is being tracked internally to be implemented some day https://github.community/t/use-env-variable-for-jobs-id-runs-on-and-jobs-id-services-image/17281/3 . – goetz Jun 12 '20 at 23:46

How to reference context values in GitHub Actions expression syntax?

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