Mastering Git Hooks: A Comprehensive Guide to Customizing Git Behavior

Introduction

Welcome to the seventh article in our Git series! In this installment, we’ll take a deep dive into Git hooks—an often-underutilized feature of Git that can greatly enhance your development workflow. Git hooks are scripts that Git executes at specific points during its lifecycle, allowing you to customize and automate various aspects of your Git experience. 

What Are Git Hooks?

Git hooks are scripts that Git runs automatically at specific times during its operations. They come in two categories: client-side and server-side hooks.

1. Client-side hooks: These hooks run on your local machine and are primarily used for tasks related to your individual repository. They reside in the `.git/hooks` directory and are not shared when you push changes to a remote repository.

2. Server-side hooks: Server-side hooks execute on the Git server, allowing you to enforce policies and checks for all users accessing the repository. Common server-side hooks include `pre-receive` and `post-receive`.

Common Uses of Git Hooks

Git hooks can be employed to address various challenges and streamline your development workflow:

1. Enforcing Coding Standards

Use `pre-commit` hooks to ensure that your code adheres to coding standards and style guidelines. For instance, you can integrate linters or formatting tools to automatically format your code before it’s committed:

!/bin/bash

Run a code formatter (e.g., Prettier)
if ! git diff --cached --name-only | xargs prettier --write; then
    echo "Commit aborted: Code formatting issues detected."
    exit 1
fi

2. Automated Testing

Trigger automated tests after each commit with a `post-commit` hook. This helps catch issues early in the development process, ensuring code quality and stability:

!/bin/bash

Run your test suite
if ! npm test; then
    echo "Tests failed. Please fix before pushing."
    exit 1
fi

3. Integration with CI/CD

Automate your CI/CD pipeline by integrating Git hooks. For example, use a `post-receive` server-side hook to trigger a build and deployment process:

!/bin/bash

Trigger CI/CD pipeline (replace with your CI/CD tool command)
/home/user/scripts/start_build.sh

4. Commit Message Validation

Ensure informative commit messages with a `commit-msg` hook. You can enforce specific conventions or check for the presence of required information:

!/bin/bash

commit_msg=$(cat "$1")

Check for a JIRA issue number in the commit message
if [[ ! $commit_msg =~ ^\[JIRA-\d+\] ]]; then
    echo "Commit message must reference a JIRA issue."
    exit 1
fi

5. Preventing Bad Commits

Stop commits that introduce errors or incomplete code from being pushed to the repository using a `pre-receive` server-side hook. This helps maintain a high level of code quality:

!/bin/bash

while read -r oldrev newrev refname; do
    Check if new commits introduce errors
    if ! git diff --name-only "$oldrev" "$newrev" | xargs eslint; then
        echo "Rejected: Commits contain linting errors."
        exit 1
    fi
done

Creating Custom Git Hooks

To create a custom Git hook, follow these steps:

1. Navigate to your Git repository’s `.git/hooks` directory.
2. Create a new executable script with the desired hook name (e.g., `pre-commit`).
3. Write your script logic according to the hook’s purpose.

Remember to make your script executable by running `chmod +x your-hook-script`.

Conclusion

Git hooks are a powerful tool for customizing and automating Git’s behavior. By leveraging them effectively, you can enforce coding standards, automate testing, integrate with CI/CD, ensure commit message quality, and maintain high code quality. Explore the possibilities of Git hooks to streamline your development process and elevate your project’s codebase to new heights.