Chapter 1: Git Basics & Repository Setup

$ git --version
git version 2.40.1
$ git config --global user.name "Your Name"
$ git config --global user.email "your.email@example.com"
$ git init my-project
Initialized empty Git repository in /my-project/.git/
$ cd my-project
$ echo "# My Project" > README.md
$ git status
Untracked files: README.md
$ git add README.md
$ git commit -m "Initial commit: add README"
[main (root-commit) a1b2c3d] Initial commit: add README
$ git log --oneline
a1b2c3d Initial commit: add README

$ git clone https://github.com/company/project.git
$ cd project
$ git checkout -b feature/add-logging
$ echo "console.log('App started');" >> app.js
$ git add app.js
$ git commit -m "feat: add startup logging"
$ git push origin feature/add-logging

$ cat > .gitignore << EOF
node_modules/
.env
*.log
dist/
.DS_Store
coverage/
EOF
$ git add .gitignore
$ git commit -m "chore: add gitignore for Node.js"
$ git rm -r --cached node_modules # Remove already tracked if any

Chapter 2: Branching & Merging Strategies

$ git branch feature/new-dashboard
$ git checkout feature/new-dashboard
Switched to branch 'feature/new-dashboard'
$ git checkout -b hotfix/critical-bug # Create and switch in one command
$ git branch -a # List all branches (local + remote)
$ git merge feature/new-dashboard
$ git branch -d feature/new-dashboard # Delete local branch after merge
$ git push origin --delete feature/new-dashboard # Delete remote branch

$ git checkout -b develop main
$ git checkout -b feature/user-auth develop
# ... work on feature ...
$ git checkout develop
$ git merge --no-ff feature/user-auth -m "Merge feature: user auth"
$ git checkout -b release/1.2.0 develop
$ # Fix release bugs, update version
$ git checkout main && git merge --no-ff release/1.2.0 -m "Release 1.2.0"
$ git tag -a v1.2.0 -m "Release version 1.2.0"
$ git push origin main --tags

$ git merge feature/payment
Auto-merging src/payment.js
CONFLICT (content): Merge conflict in src/payment.js
$ git status # Shows both modified
$ cat src/payment.js
<<<<<<< HEAD
function processPayment(amount) { return amount * 1.1; }
=======
function processPayment(amount, tax=0.1) { return amount * (1 + tax); }
>>>>>>> feature/payment
$ # Edit file to keep both improvements:
function processPayment(amount, tax=0.1) { return amount * (1 + tax); }
$ git add src/payment.js
$ git commit -m "merge: resolve payment processor conflict"

Chapter 3: Undoing Changes & Recovery

$ git restore file.txt # Discard unstaged changes
$ git restore --staged file.txt # Unstage but keep changes
$ git reset --soft HEAD~1 # Undo last commit, keep changes staged
$ git reset --hard HEAD~1 # ⚠️ Completely remove last commit (dangerous)
$ git revert HEAD # Creates new commit that undoes last commit (safe)
$ git reflog
a1b2c3d HEAD@{0}: commit: fix login bug
e4f5g6h HEAD@{1}: commit: add feature
...
$ git reset --hard e4f5g6h # Recover to previous state

$ git log --oneline | head -5
abc1234 fix: add API key (SECRET!)
def5678 previous good commit
$ git rebase -i HEAD~2
# Change 'pick' to 'edit' for abc1234
$ git restore --staged config.js
$ echo "API_KEY=CHANGE_ME" > config.js
$ git add config.js && git commit --amend --no-edit
$ git rebase --continue
$ git push --force-with-lease origin main

$ git reflog | grep "checkout: moving from feature"
a1b2c3d HEAD@{12}: checkout: moving from feature/new-ui to main
$ git checkout -b feature/new-ui a1b2c3d
Switched to a new branch 'feature/new-ui'
$ git log --oneline -3
# Branch restored with all commits!

Chapter 4: GitHub Collaboration & Pull Request Workflow

$ git remote add origin https://github.com/user/repo.git
$ git push -u origin main
$ git checkout -b feature/awesome
$ git push origin feature/awesome
# Now open Pull Request on GitHub.com
$ git pull --rebase origin main # Sync before merging PR
$ git push origin feature/awesome --force-with-lease

# On GitHub: Fork the repository
$ git clone https://github.com/YOUR_USERNAME/upstream-repo.git
$ cd upstream-repo
$ git remote add upstream https://github.com/original/upstream-repo.git
$ git checkout -b fix/typo
$ # Make changes, commit, push
$ git push origin fix/typo
# Create PR from YOUR_USERNAME/fix/typo → original/main
$ git fetch upstream
$ git checkout main && git merge upstream/main

# .github/workflows/pr-labeler.yml
name: PR Labeler
on: pull_request
jobs:
  label:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/labeler@v4
        with:
          repo-token: "${{ secrets.GITHUB_TOKEN }}"

Chapter 5: GitHub Actions Fundamentals

# .github/workflows/ci.yml
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 ci
      - name: Run tests
        run: npm test

jobs:
  test:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        node-version: [16, 18, 20]
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: ${{ matrix.node-version }}
      - run: npm ci && npm test

Chapter 6: CI/CD Pipeline Design

name: Complete CI
on: [push, pull_request]
jobs:
  ci:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '18'
          cache: 'npm'
      - run: npm ci
      - run: npm run lint
      - run: npm run test:coverage
      - name: Upload coverage
        uses: codecov/codecov-action@v3

Chapter 7: Testing & Linting Automation

- name: Lint & Format Check
  run: |
    npm run lint
    npm run format:check
- name: Run Unit Tests
  run: npm run test:unit
- name: Run Integration Tests
  run: npm run test:integration

Chapter 8: Docker Build & Push Actions

- name: Login to Docker Hub
  uses: docker/login-action@v3
  with:
    username: ${{ secrets.DOCKER_USERNAME }}
    password: ${{ secrets.DOCKER_TOKEN }}
- name: Build and push
  uses: docker/build-push-action@v5
  with:
    push: true
    tags: user/app:latest,user/app:${{ github.sha }}

Chapter 9: Secrets Management & Security

# Store secrets in GitHub → Settings → Secrets and variables → Actions
- name: Deploy to AWS
  env:
    AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
    AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
  run: |
    aws s3 sync build/ s3://my-bucket
    aws cloudfront create-invalidation --distribution-id ${{ secrets.CF_DIST_ID }} --paths "/*"

Chapter 10: Production Deployment Workflows

name: Deploy to Production
on:
  workflow_dispatch:
    inputs:
      version:
        description: 'Version to deploy'
        required: true
jobs:
  deploy:
    runs-on: ubuntu-latest
    environment: production
    steps:
      - uses: actions/checkout@v4
      - name: Deploy to Kubernetes
        run: |
          kubectl set image deployment/myapp app=myapp:${{ github.event.inputs.version }}
          kubectl rollout status deployment/myapp