Git Hooks

What are Git Hooks?

Git hooks are scripts that run automatically when certain Git events happen, like making a commit or pushing code.

Why Use Hooks?

Hooks help you automate repetitive tasks, enforce coding standards, and catch problems early.

For example, you can:

• Run tests before every commit or push
• Check code style automatically
• Block bad commit messages
• Enforce rules for everyone on your team

Where Do Hooks Live?

Hooks are stored in .git/hooks inside your repository.

By default, you'll see sample scripts ending with .sample.

ls .git/hooks
applypatch-msg.sample      pre-commit.sample          pre-receive.sample
commit-msg.sample          pre-merge-commit.sample    push-to-checkout.sample
fsmonitor-watchman.sample  prepare-commit-msg.sample  sendemail-validate.sample
post-update.sample         pre-push.sample            update.sample
pre-applypatch.sample      pre-rebase.sample

How to Enable a Hook

To enable a hook, remove the .sample extension and make the script executable.

For example, to enable pre-commit:

mv .git/hooks/pre-commit.sample .git/hooks/pre-commit
chmod +x .git/hooks/pre-commit

On Windows, also rename the file to exactly pre-commit, with no file extension. Git for Windows runs hook scripts that start with #!/bin/sh using its bundled shell, so the same script works on every system.

Types of Hooks

There are many types of hooks, but the most common are:

• pre-commit
• commit-msg
• pre-push
• pre-receive
• post-receive

pre-commit Hook

The pre-commit hook runs before you make a commit.

You can use it to check code style, run tests, or stop a commit if something is wrong.

#!/bin/sh
# Stop commit if any .js file has "console.log"
grep -r 'console.log' *.js && {
  echo "Remove console.log before committing!"
  exit 1
}

commit-msg Hook

The commit-msg hook checks or edits the commit message.

For example, it can block commits without a ticket number.

#!/bin/sh
# Block commit if message does not contain a ticket number
if ! grep -qE 'JIRA-[0-9]+' "$1"; then
  echo "Commit message must have a ticket number (e.g. JIRA-123)"
  exit 1
fi

pre-push Hook

The pre-push hook runs before you push code to a remote.

You can use it to run tests or checks before sharing code.

#!/bin/sh
npm test || exit 1

Server-side Hooks

Some hooks (like pre-receive) run on the Git server, not your computer.

These can enforce rules for everyone who pushes to the repository.

#!/bin/sh
# Block pushes to the main branch
if grep -q ' refs/heads/main$'; then
  echo "Pushing to main is not allowed"
  exit 1
fi

Custom Hooks

You can write any custom script as a hook.

Just put it in .git/hooks and make it executable.

#!/bin/sh
echo "Hello from my custom hook!"

Debugging and Best Practices

• Make sure your hook script is executable (chmod +x scriptname).
• Add echo statements to see what your script is doing.
• Check the exit code: exit 0 means success, exit 1 means fail.
• Name hooks exactly (like pre-commit, with no file extension). Git for Windows runs #!/bin/sh scripts with its bundled shell.
• Keep hooks simple and fast; slow hooks slow down your workflow.
• Share useful hooks with your team (but remember: hooks are not versioned by default).