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Chapter 20 — Git Hooks

Git hooks are scripts that run automatically at specific points in the Git workflow. They live in .git/hooks/.

Available Hooks

Hook                  When It Runs
────────────────────────────────────────────────────
pre-commit            Before a commit is created
prepare-commit-msg    After default message, before editor opens
commit-msg            After you write the message (validate it)
post-commit           After a commit is created
pre-push              Before a push
pre-rebase            Before a rebase
post-merge            After a merge
post-checkout         After checkout / switch

Your First Hook

Example: pre-commit hook that runs linting

cat > .git/hooks/pre-commit << 'EOF'
#!/bin/bash
echo "Running linter..."
npm run lint

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

echo "✅ Lint passed."
EOF

chmod +x .git/hooks/pre-commit

Now try committing:

git commit -m "Test hook"
Running linter...
✅ Lint passed.
[main a1b2c3d] Test hook

🧠 What happened? The hook ran before the commit. If it exits with a non-zero code, the commit is aborted.

Example: commit-msg hook to enforce format

cat > .git/hooks/commit-msg << 'EOF'
#!/bin/bash
MSG=$(cat "$1")
PATTERN="^(feat|fix|docs|style|refactor|test|chore|perf|ci|build)(\(.+\))?: .{1,50}"

if ! echo "$MSG" | grep -qE "$PATTERN"; then
    echo "❌ Commit message does not follow Conventional Commits format."
    echo "   Expected: <type>(optional scope): <description>"
    echo "   Example:  feat(auth): add login endpoint"
    exit 1
fi
EOF

chmod +x .git/hooks/commit-msg
git commit -m "stuff"
❌ Commit message does not follow Conventional Commits format.
   Expected: <type>(optional scope): <description>
   Example:  feat(auth): add login endpoint

git commit -m "feat: add user model"
[main b2c3d4e] feat: add user model

Example: pre-push hook to run tests

cat > .git/hooks/pre-push << 'EOF'
#!/bin/bash
echo "Running tests before push..."
npm test

if [ $? -ne 0 ]; then
    echo "❌ Tests failed. Push aborted."
    exit 1
fi
EOF

chmod +x .git/hooks/pre-push

The Problem: Hooks Aren't Shared

.git/hooks/ is not tracked by Git, so hooks don't travel with the repository. Your teammates won't have them.

Solution 1: Use a hooks directory in the repo

mkdir .githooks

# Move hooks there
mv .git/hooks/pre-commit .githooks/

# Tell Git to use this directory
git config core.hooksPath .githooks

# Commit the hooks
git add .githooks/
git commit -m "chore: add shared git hooks"

Solution 2: Use a tool like Husky (Node.js projects)

npm install --save-dev husky
npx husky init
# Create a pre-commit hook
echo "npm run lint" > .husky/pre-commit

Now every developer who runs npm install gets the hooks automatically.

Bypassing Hooks

Example: Skip hooks for a single commit

git commit --no-verify -m "WIP: quick save"

Example: Skip hooks for a push

git push --no-verify

⚠️ Use sparingly. If you're bypassing hooks often, the hooks might be too strict or too slow.

← Chapter 19: Commit Messages · Next: Chapter 21 — Tips & Tricks →