GitHub Actions Cheatsheet

Basics

Use this GitHub Actions reference while you build software engineering projects, review code for technical interview prep, or polish examples for a software engineer resume.

What is GitHub Actions

GitHub Actions is a CI/CD platform built into GitHub. Workflows run in response to events (push, PR, schedule, etc.) on GitHub-hosted or self-hosted runners.

Use this cheatsheet after a snippet works in an online code editor, Python online compiler, JavaScript playground, or C++ online compiler. Actions turns that browser experiment into repeatable CI so every push can install dependencies, run tests, and catch regressions.

Key concepts:

Term	Description
Workflow	YAML file in `.github/workflows/` — the top-level unit
Event	What triggers the workflow (`push`, `pull_request`, `schedule`, …)
Job	A group of steps that run on the same runner
Step	A single shell command or reusable Action
Action	A reusable unit — from Marketplace or your own repo
Runner	The VM/container that executes the job

File Location

Workflows live in .github/workflows/ at the root of your repo.

.github/
  workflows/
    ci.yml
    deploy.yml
    nightly.yml

Any .yml or .yaml file in that directory is picked up automatically.

From Online Compiler to CI

A browser compiler is great for the first proof. Use Hack University's Python online compiler, JavaScript playground, or C++ online compiler to run code online, then move the same solution into a repo and let GitHub Actions repeat the check on every push.

Starting point	GitHub Actions follow-up
One-file algorithm	Add a unit test job that runs the same cases on `push`
Small web demo	Add install, lint, and build steps before deploy
Portfolio project	Upload artifacts and keep failing logs easy to inspect

Minimal Workflow

name: Hello World

on: push

jobs:
  greet:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Hello, GitHub Actions!"

Full Skeleton

name: CI

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest

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

      - name: Set up Node
        uses: actions/setup-node@v4
        with:
          node-version: 20

      - name: Install dependencies
        run: npm ci

      - name: Run tests
        run: npm test

Workflow Anatomy

name          →  display name in the Actions UI
on            →  event(s) that trigger the workflow
env           →  workflow-level env vars (optional)
defaults      →  default shell/working-directory (optional)
jobs          →  map of job IDs → job definitions
  <job-id>:
    runs-on   →  runner label
    steps     →  ordered list of steps
      - uses  →  reference an Action
      - run   →  run shell commands

Context Objects (Quick Reference)

Context	Common properties
`github`	`.event_name`, `.ref`, `.sha`, `.actor`, `.repository`
`env`	workflow/job/step environment variables
`vars`	repo/org configuration variables
`secrets`	encrypted secrets
`runner`	`.os`, `.arch`, `.temp`
`job`	`.status`
`steps.<id>`	`.outputs.<name>`, `.conclusion`
`matrix`	current matrix values

Access via ${{ github.sha }}, ${{ secrets.MY_SECRET }}, etc.

CLI — GitHub CLI for Actions

# List workflow runs
gh run list

# Watch a run in real time
gh run watch <run-id>

# View logs
gh run view <run-id> --log

# Re-run failed jobs only
gh run rerun <run-id> --failed-only

# Manually trigger a workflow (workflow_dispatch)
gh workflow run ci.yml --ref main

# List workflows
gh workflow list

# Enable / disable a workflow
gh workflow enable ci.yml
gh workflow disable ci.yml

Permissions

Default token permissions are set at the repo or org level. Override per workflow or job:

permissions:
  contents: read
  pull-requests: write
  issues: write

Minimum-privilege: set permissions: read-all at workflow level, then grant write only where needed per job.