Hooks & Automation

Quick Summary

Git hooks are scripts that run automatically when specific Git events occur (commit, push, merge, etc.). They let you enforce code quality (lint before commit), run tests (before push), and automate repetitive tasks — all without relying on CI/CD.

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Available Hooks

Hook	Trigger	Common Use
pre-commit	Before commit is created	Lint, format, check secrets
commit-msg	After message is entered	Validate commit message format
pre-push	Before push to remote	Run tests
post-merge	After merge completes	Install dependencies
post-checkout	After branch switch	Setup environment
prepare-commit-msg	Before editor opens	Auto-populate message template

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Creating a Hook

Hooks live in .git/hooks/. Create a file with the hook name (no extension) and make it executable:

# Create a pre-commit hook
nano .git/hooks/pre-commit

#!/bin/sh
# pre-commit hook: run linter before allowing commit

echo "Running linter..."
npm run lint

if [ $? -ne 0 ]; then
    echo "❌ Lint failed. Fix errors before committing."
    exit 1  # Block the commit
fi

echo "✅ Lint passed."
exit 0  # Allow the commit

# Make it executable
chmod +x .git/hooks/pre-commit

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Useful Hook Examples

Pre-commit: Check for Debug Statements

#!/bin/sh
# Block commits containing console.log or debugger

BLOCKED=$(git diff --cached --name-only | xargs grep -l "console\.log\|debugger" 2>/dev/null)

if [ -n "$BLOCKED" ]; then
    echo "❌ Found debug statements in:"
    echo "$BLOCKED"
    echo "Remove console.log/debugger before committing."
    exit 1
fi

Commit-msg: Enforce Conventional Commits

#!/bin/sh
# Require conventional commit format

MSG=$(cat "$1")
PATTERN="^(feat|fix|docs|style|refactor|test|chore|perf)(\(.+\))?: .{3,}"

if ! echo "$MSG" | grep -qE "$PATTERN"; then
    echo "❌ Commit message must follow Conventional Commits format:"
    echo "   feat: add login page"
    echo "   fix(auth): resolve timeout issue"
    exit 1
fi

Pre-push: Run Tests

#!/bin/sh
echo "Running tests before push..."
npm test

if [ $? -ne 0 ]; then
    echo "❌ Tests failed. Fix before pushing."
    exit 1
fi

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Sharing Hooks with the Team

Git hooks live in .git/hooks/ which is not tracked by Git. Solutions:

Option 1: Husky (Node.js projects)

# Install Husky
npm install --save-dev husky

# Initialize
npx husky init

# Add a pre-commit hook
echo "npm run lint" > .husky/pre-commit

package.json:

{
  "scripts": {
    "prepare": "husky"
  }
}

Option 2: Custom hooks directory

# Store hooks in a tracked directory
mkdir -p .githooks

# Configure Git to use it
git config core.hooksPath .githooks

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Best Practices

• Keep hooks fast — slow pre-commit hooks frustrate developers
• Use Husky or core.hooksPath — ensure the whole team uses the same hooks
• Don't replace CI/CD — hooks are local; CI/CD is the authoritative check
• Allow bypass for emergencies — git commit --no-verify skips hooks
• Test hooks — a broken hook can block all commits

What's Next

1. Common Errors — Fix frequent Git mistakes
2. Undoing Changes — Undo commits, merges, and staged changes