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

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 }}"

Answer 2

Difficult to say without running it, but I would say you need to use the output in the second step by assigning it to a variable, something like:
env:
OUTPUT: ${{ steps.id.outputs.arr }}
Then you use $OUTPUT as an environment variable inside the action.
The problem with that particular action is that it takes one commit at a time. But you can check out the code, it's a shell script. You can fork it from line 15 and make it split input and run a loop over it, applying eslint to every one of them.