Git Hooks & Automation

Git Hooks are scripts that Git executes before or after events such as commit, push, and receive. They are a powerful way to automate your workflow and enforce project standards.

Where are Hooks Stored?

Hooks are stored in the .git/hooks directory of every Git repository. By default, this directory contains several example scripts.

Command:

ls .git/hooks

Result:

applypatch-msg.sample      pre-push.sample
commit-msg.sample          pre-rebase.sample
post-update.sample         pre-receive.sample
pre-applypatch.sample      prepare-commit-msg.sample
pre-commit.sample          update.sample

Client-Side vs. Server-Side Hooks

1. Client-Side Hooks: Run on your local machine (e.g., pre-commit, pre-push).
2. Server-Side Hooks: Run on the server (e.g., GitHub, GitLab) when receiving pushed commits (e.g., pre-receive, post-receive).

The pre-commit Hook

The pre-commit hook runs before you even type a commit message. It's perfect for:

• Running linters (ESLint, Prettier)
• Running unit tests
• Checking for secrets (API keys) in code

Example: Simple Pre-commit Linter

Create a file at .git/hooks/pre-commit:

#!/bin/bash
 
echo "Running pre-commit checks..."
 
# Check for 'TODO' in code
if grep -q "TODO" . -r --exclude-dir=.git; then
    echo "ERROR: You have TODOs in your code. Please fix them before committing."
    exit 1
fi
 
echo "Checks passed!"
exit 0

Action:

chmod +x .git/hooks/pre-commit
git commit -m "Add new feature"

Result (if TODO found):

Running pre-commit checks...
ERROR: You have TODOs in your code. Please fix them before committing.

The pre-push Hook

Runs before git push sends data to the remote. Use this for "heavy" tasks like integration tests or build checks.

Using Husky (Modern Workflow)

In the JavaScript/DevOps ecosystem, Husky is the industry standard for managing hooks because Git hooks in .git/hooks are NOT committed to the repository. Husky allows you to share hooks with your team.

Command:

npx husky-init && npm install
npx husky add .husky/pre-commit "npm test"

Result: This creates a .husky/ directory that is tracked by Git, ensuring every developer runs the same checks.

DevOps Use Cases for Hooks

1. Security: Run gitleaks or trufflehog to prevent secrets from being committed.
2. Quality: Enforce conventional commit messages (e.g., feat:, fix:) using commit-msg hooks.
3. Efficiency: Automatically update documentation or build artifacts.

Summary

• Hooks live in .git/hooks/.
• pre-commit is the most common hook.
• Use Husky to share hooks with your team.
• Hooks are your first line of defense in a CI/CD pipeline.