Using an array of values to repeat a step in GitHub Actions workflow

Question

I am trying to create a GitHub Actions workflow which would collect specific paths changed in last commit and run a step for each of collected paths, if any.

Currently, in my workflow I'm creating an array of paths, but I'm not sure how to proceed with my array:

name: Test

on:
  push

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v1

      # This step will create "an array" of strings, e.g. "path1 path2 path3"
      - name: array
        id: arr
        run: |
          arr=()
          for i in "$(git diff-tree --no-commit-id --name-only -r ${{ github.sha }})"
          do
            if [[ $i == *"path1"* ]]; then
              arr+=("path1")
            fi
            if [[ $i == *"path2"* ]]; then
              arr+=("path2")
            fi
          done
          echo ::set-output name=arr::${arr[@]}

      # How to run this step by iterating the `${{ steps.arr.outputs.arr }}`?
      - name: reviewdog-lint
        uses: reviewdog/action-eslint@v1
        with:
          github_token: ${{ secrets.GITHUB_TOKEN }}
          reporter: github-pr-review
          eslint_flags: 'my_project/some_folder/${{ SINGLE_PATH }}/'  # `SINGLE_PATH` would be a path from the array

Is something like this even possible in the first place? If not, what would be recommended way to loop through some values and use them as arguments in other workflow steps?

Answer 1

There is some support for this in Github Actions. There is a very good tutorial here that explains how to do it in detail, but essentially what you'll do is split the steps into two jobs. The first job will output a JSON object that will serve as the input to the matrix of the second job.

Here's a simple example:

jobs:

  setup:
    runs-on: ubuntu-latest
    outputs:
      matrix: ${{ steps.matrix.outputs.value }}
    steps:
      - id: matrix
        run: |
          echo '::set-output name=value::[\"a\", \"b\", \"c\"]'
  build:
    needs: [ setup ]
    runs-on: ubuntu-latest
    strategy:
      matrix:
        value: ${{fromJson(needs.setup.outputs.matrix)}}
    steps:
      - run: |
          echo "${{ matrix.value }}"