Part 8: Git Hooks and Customization

Introduction

Git hooks are scripts that run automatically when certain events occur in your Git workflow. They are useful for automating tasks, enforcing coding standards, and integrating with external tools. Customizing Git with hooks can improve your development process and ensure consistency across your team.

1. What Are Git Hooks?

Git hooks are local scripts triggered by specific Git events, such as committing changes, pushing to a repository, or merging branches. They are located in the .git/hooks directory of a repository and can be either client-side or server-side:

Client-side hooks: Run on operations like committing and merging.
Server-side hooks: Run on server operations like receiving pushed commits.

2. Common Git Hooks and Their Uses

Pre-commit Hook

Runs before a commit is created. It’s often used to:

Check code formatting.
Run tests or linters.
Prevent certain files from being committed.

Example pre-commit hook (.git/hooks/pre-commit):

#!/bin/bash
# Run a linter before committing
npm run lint

# Exit with a non-zero status to cancel the commit if linting fails
if [ $? -ne 0 ]; then
  echo "Linting failed. Commit aborted."
  exit 1
fi

Make sure the script is executable:

$ chmod +x .git/hooks/pre-commit

Commit-msg Hook

Checks the commit message for a specific format or convention. This is useful for enforcing team standards for commit messages.

Example commit-msg hook:

#!/bin/bash
# Check if the commit message follows a pattern
MESSAGE=$(cat $1)

if ! [[ $MESSAGE =~ ^\[JIRA-[0-9]+\]: ]]; then
  echo "Commit message must start with '[JIRA-XXXX]:'"
  exit 1
fi

Pre-push Hook

Runs before git push is executed. It can be used to:

Run tests to ensure that code is not pushed with errors.
Validate branch names.

3. Creating and Managing Git Hooks

To create a Git hook:

Navigate to the .git/hooks directory.
Create or edit the hook file (e.g., pre-commit, commit-msg).
Ensure the file is executable.

Git hooks are not shared by default. To distribute hooks across a team, consider these approaches:

Include hooks in the repository: Place hooks in a directory like scripts/hooks/ and use a script to copy them to .git/hooks.
Use a tool like Husky for JavaScript projects. Husky integrates hooks with your project’s package.json and runs them using Node.js.

Example: Setting Up Husky

# Install Husky
$ npm install husky --save-dev

# Enable Git hooks
$ npx husky install

# Add a pre-commit hook
$ npx husky add .husky/pre-commit "npm run lint"

This setup runs npm run lint before each commit.

5. Customizing Git Configuration

Git can be customized using configuration files located at different levels:

System-level (/etc/gitconfig): Applies to all users on the system.
Global-level (~/.gitconfig): Applies to the current user.
Repository-level (.git/config): Applies to the specific repository.

Useful Git Config Customizations

# Set a default text editor for Git
$ git config --global core.editor "code --wait"

# Enable colored output for better readability
$ git config --global color.ui auto

# Create an alias for common commands
$ git config --global alias.st status
$ git config --global alias.co checkout

6. Practical Example: Pre-commit Hook for Code Formatting

Create a pre-commit hook to run Prettier before committing:

#!/bin/bash
npx prettier --check "src/**/*.{js,jsx,ts,tsx}"

if [ $? -ne 0 ]; then
  echo "Code formatting issues found. Please run 'npx prettier --write' to fix them."
  exit 1
fi

Make the script executable:

$ chmod +x .git/hooks/pre-commit

Recap

Git hooks automate tasks in your development workflow.
Pre-commit, commit-msg, and pre-push hooks can be used for code checks, message validation, and more.
Husky helps integrate hooks into projects easily.
Custom Git configurations improve workflow efficiency with aliases and color settings.

Next Steps

In the next part, we’ll cover Rewriting History with Git, including git rebase, git cherry-pick, and git filter-branch, to refine and edit commit history.

Stay tuned for Part 9: "Rewriting History with Git."