How to use env variable on workflow level github-actions

Question

I have a simple workflow:

name: Test CI

env:
  path_to_watch_for_commits: 'testdir/testfile'

on:
  push:
    branches:
      - master
    paths:
      - ${{ env.path_to_watch_for_commits }}

  workflow_dispatch:

jobs:
  build:
    runs-on:  ubuntu

    steps:
      - uses: actions/checkout@v2

I want to use variable path_to_watch_for_commits in paths. But this syntax is wrong. Also i try ${{ path_to_watch_for_commits }} and $path_to_watch_for_commits with no results. What am i doing wrong?

Answer 1

There is a Naming conventions for environment variables explaining that:

Any new environment variables you set that point to a location on the filesystem should have a _PATH suffix. The HOME and GITHUB_WORKSPACE default variables are exceptions to this convention because the words "home" and "workspace" already imply a location.

Regarding the use of environment variables at different levels inside the workflow, here is an example with WORKFLOW, JOB and STEP variables:

name: Example

on: [push, workflow_dispatch]

env:
  WORKFLOW_VARIABLE: WORKFLOW

jobs:
  test:
    runs-on: ubuntu-latest
    env:
      JOB_VARIABLE: JOB
    steps:
      - name: Run Commands with various variables
        if: ${{ env.WORKFLOW_VARIABLE == 'WORKFLOW' }}
        env:
          STEP_VARIABLE: STEP
        run: |
          echo "Hello World"
          echo "This is the $WORKFLOW_VARIABLE environment variable"
          echo "This is the $JOB_VARIABLE environment variable"
          echo "This is the $STEP_VARIABLE environment variable"

---

Regarding the possibility of the behaviour you want to achieve in your workflow, you can't set variables at the workflow and use them as paths on the same level, because:

Variables are substituted in the runner operating system after the job is sent to the runner.

Reference

A workaround could be to trigger the workflow every time on push event, using the paths-filter action with an if conditional to execute specific steps if it match your paths.

It's not the best solution regarding optimisation, but it will work.