GitHub Actions can be used to do something whenever something happens in one of your GitHub repositories. If you are not familiar with GitHub Actions, check out my article Getting Started with GitHub Actions.

For example, let's say you have a repository named my-repo that contains 2 files, foo.jpg and bar.jpg, perhaps like this.

• https://github.com/JohnDoe/my-repo/blob/main/images/foo.jpg
• https://github.com/JohnDoe/my-repo/blob/main/images/bar.jpg

The ${{ github.workspace }} variable can be used to list the files in your repository.

name: GitHub Action
run-name: ${{ github.workflow }} run by ${{ github.actor }}
on:
  push:
    branches:
      - main
jobs:
  github-action-job:
    runs-on: ubuntu-latest
    steps:
      - name: Checking out the repository code . . .
        uses: actions/checkout@v4

      - name: List files in the repository
        run: |
          ls ${{ github.workspace }}

And here is example of how to list all changed files using tj-actions/changed-files

name: GitHub Action
run-name: ${{ github.workflow }} run by ${{ github.actor }}
on:
  push:
    branches:
      - main
jobs:
  github-action-job:
    runs-on: ubuntu-latest
    steps:      
      - name: Checking out the repository code . . .
        uses: actions/checkout@v4

      - name: Get changed files
        id: changed-files
        uses: tj-actions/changed-files@v40

      - name: List all changed files
        run: |
          for file in ${{ steps.changed-files.outputs.all_changed_files }}; do
            echo "$file was changed"
          done

Often, there will be certain files you'll want to ignore, such as README.md and files in the .github/workflows directory. Files can be ignored by including files_ignore.

jobs:  
  get_changed_files:
    runs-on: ubuntu-latest
    steps:
      - name: Checking out the repository code
        uses: actions/checkout@v4

      - name: Get changed files excluding README.md and files in the .github/workflows directory
        id: changed-files
        uses: tj-actions/changed-files@v40
        with:
          separator: ","   
          files_ignore: |
            README.md
            .github/workflows/*

      - name: changed files
        run: |
          echo "changed files = ${{ steps.changed-files.outputs.all_changed_files }}"

      - name: changed files count
        run: |
          echo "changed files count = ${{ steps.changed-files.outputs.all_changed_files_count }}"

    outputs:
      changed_files_count: ${{ steps.changed-files.outputs.all_changed_files_count }}

Which should return something like this.

And here is how to get the changed files as JSON.

name: GitHub Action
run-name: ${{ github.workflow }} run by ${{ github.actor }}
on:
  push:
    branches:
      - main
jobs:
  github-action-job:
    runs-on: ubuntu-latest
    steps:      
      - name: Checking out the repository code . . .
        uses: actions/checkout@v4

      - name: Get changed files
        id: changed-files
        uses: tj-actions/changed-files@v40
        with:
          json: true
          escape_json: true

      - name: List all changed files as escaped JSON
        run: echo '${{ steps.changed-files.outputs.all_changed_files }}'

Which should output something like this.

echo 'files = ["path/to/foo.txt"]["path/to/bar.txt"]