main.yml

name: Check Changed Files in PR

on:
  pull_request:
    types: [opened, synchronize]

jobs:
  check_files:
    runs-on: ubuntu-latest
    
    steps:
    - name: Checkout code
      uses: actions/checkout@v2
      
    - name: Count changed files
      id: count_files
      run: |
        git fetch --prune --unshallow
        num_changed_files=$(git diff --name-only origin/${{ github.base_ref }} ${{ github.sha }} | wc -l)
        echo "::set-output name=num_changed_files::$num_changed_files"
        
        
        
    - name: Check if only 1 file changed
      run: |
        changed_files=${{ steps.count_files.outputs.num_changed_files }}
        if [ $changed_files -ne 1 ]; then
          echo "More than 1 file changed. Exiting."
          exit 1
        else
          echo "Exactly 1 file changed. Proceeding."
        fi