Explain the basic structure of a GitHub Actions workflow file.

A workflow file is YAML in .github/workflows/ with three layers: events that trigger it, jobs it runs, and steps inside each job. Steps run in order.

name: CI Pipeline
on: [push, pull_request]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '18'
      - name: Install dependencies
        run: npm install
      - name: Run tests
        run: npm test

The keys in this file:

• name is an optional name for the workflow.
• on lists the events that trigger it, here every push and pull request.
• jobs holds the jobs. Each job is a set of steps that runs on the same runner, and by default jobs run in parallel.
• runs-on picks the runner environment, here ubuntu-latest.
• steps are the individual tasks inside a job.
• uses references a pre-built action, such as actions/checkout.
• run executes a shell command.