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What are git hooks?

Straight from the horse's mouth:

Hooks are programs you can place in a hooks directory to trigger actions at certain points in git’s execution.

• git-scm.com

How to quickly add a git hook?

Inside your git repository:

1. Open .git/hooks/pre-commit.

2. Add the following sample script:

#!/usr/bin/env bash

echo -e "\n\nPre-commit hook has been triggered\n\n"

3. Make is executable (if it isn't already).

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

4. Profit! Try running the git commit command in that repo.

A more useful example maybe?

Sure, I have a pre-commit git hook written that... Well, let me just show you:

#!/bin/sh

set -euo pipefail

STAGED=$(git diff --cached --name-only | xargs)

# Lint
yarn eslint --fix $STAGED
# Format
yarn prettier --write $STAGED
# Type check
yarn tsc --noEmit
# Test
yarn jest
# Re-stage
git add $STAGED

This little script does linting, formatting, type checking, and unit testing before the staged files are ready to commit. As a side note, see line 5 to get only staged files. The pipefail command runs the script in "strict mode"; see Shell Notes for more details.

What's this core.hooksPath?

As above, by default, hooks are placed in .git/hooks directory. We can have them hooks in another directory inside the repo (e.g. ./hooks) and as such ensure that everyone gets a copy of it when they clone a repo. Then you can have an initialization script (like 'preinstall' for package.json) that does the git config core.hooksPath hooks and voila! hooks installed just like that.

Must they always be bash scripts?

NO. You can have any script that executes. Here's another example of pre-commit in Nodejs:

#!/usr/bin/env node

console.log("\n\nPre-commit hook in Nodejs has been triggered\n\n")

And Python:

#!/usr/bin/env python

print("\n\nPre-commit hook in Python has been triggered\n\n")

Alright, where can I learn more?

Here ya go:

• git-scm

• githooks

• Atlassian tutorial

Thanks for reading and happy hacking!

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