In this module, we will explore Git hooks, which are scripts that Git automatically executes in response to certain repository events. Hooks are extremely useful for automating tasks such as code verification, running tests, and continuous deployment.

What are Git hooks?

Git hooks are scripts that Git automatically executes before or after important events, such as commits, pushes, and merges. There are two main types of hooks:

• Client-side hooks: Affect local operations like commits and merges.
• Server-side hooks: Run on the server during network operations like receiving pushes.

Location of hooks

Hooks are located in the .git/hooks directory of your repository. Each hook is a script file (usually Shell, Python, Ruby, etc.) and must be executable for Git to run them.

Client-side hooks

Pre-commit

Runs before a commit is made. You can use it to validate the commit message, check code style, or run tests.

Example of pre-commit that prevents commits with empty messages:

sh

1. Create a file named pre-commit in the .git/hooks directory.
2. Add the above code.
3. Make the script executable:

   bash
   

Commit-msg

Runs after the commit message is entered, but before the commit completes. It can be used to validate the commit message format.

Example of commit-msg that validates that the commit message is not empty:

sh

1. Create a file named commit-msg in the .git/hooks directory.
2. Add the above code.
3. Make the script executable:

   bash
   

Server-side hooks

Pre-receive

Runs on the server before accepting a push. Useful for validating changes before accepting them into the remote repository.

Basic example of pre-receive:

sh

1. On the server, create a file named pre-receive in the hooks directory of your remote repository.
2. Add the above code.
3. Make the script executable:

   bash
   

Post-receive

Runs after changes have been accepted on the server. Useful for continuous deployment or notifications.

Example of post-receive that deploys the code to a web server:

sh

1. On the server, create a file named post-receive in the hooks directory of your remote repository.
2. Add the above code.
3. Make the script executable:

   bash
   

Practical examples

Pre-commit hook that checks code style with eslint

1. First, install eslint in your project:

   bash
   

2. Create the pre-commit file in .git/hooks:

   sh
   

3. Make the script executable:

   bash
   

Post-receive hook to send Slack notifications

1. Set up the Slack webhook.
2. Create the post-receive file in the hooks directory of the remote repository:

   sh
   

3. Make the script executable:

   bash
   

Best practices

• Keep hooks versioned: Store your hook scripts in the repository (e.g., in a .githooks folder) so all collaborators can access them.
• Document your hooks: Provide clear instructions on how to install and use the hooks.
• Testing in hooks: Ensure that the scripts in the hooks do not introduce faults in your workflow.

Configuring hooks through core.hooksPath

You can set up a custom directory for hooks:

1. Create a folder to store your hooks (e.g., .githooks).
2. Move your hook scripts to this folder.
3. Configure core.hooksPath to use this folder:

   bash
   

With these techniques and examples, you can start automating repetitive tasks and integrating different tools into your development workflow using Git hooks. In the next module, we will learn about continuous integration with GitHub Actions.