Get and use output from docker in GHA

get-output-from-docker.yml

name: Get Output from Docker

on:
  workflow_dispatch:
  push:
    branches: [ main ]

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
      - name: Checkout code
        uses: actions/checkout@v4

      - name: Prepare output file
        run: |
          touch output.env
        
      - name: Run Alpine docker container
        id: run-docker
        run: |
          docker run --rm \
            -v ${{ github.workspace }}/output.env:/output.env \
            alpine \
            /bin/sh -c "echo 'hello=\"hello world\"' >> /output.env && echo 'thing=\"some thing\"' >> /output.env && echo 'test=\"this\"' >> /output.env"
        
      - name: Load and use output as environment variable
        run: |
          source output.env
          echo "hello is $hello"
          echo "thing is $thing"
          echo "test is $test"