Introduction

Git hooks are super powerful for automating tasks and enforcing coding standards in a Git repository. One common use case for Git hooks is to run automated tests and code analysis tools before allowing a commit to proceed. In this article we’ll cover pre-commit hooks, how to skip them and how to set up a pre-commit hook to run Rubocop, a Ruby code analysis tool.

What is Rubocop?

Rubocop is a static code analysis tool for Ruby that checks code for style and security issues. It’s a popular tool among Ruby developers to ensure their code follows the Ruby style guide and best practices. Rubocop can be run manually but integrating it with a pre-commit hook ensures code is checked automatically before each commit.

Copy this into .git/hooks/pre-commit (remove .sample)

#!/usr/bin/env ruby

require 'english'
require 'rubocop'

ADDED_OR_MODIFIED = /A|AM|^M/.freeze

changed_files = `git status --porcelain`.split(/\n/).
    select { |file_name_with_status|
      file_name_with_status =~ ADDED_OR_MODIFIED
    }.
    map { |file_name_with_status|
      file_name_with_status.split(' ')[1]
    }.
    select { |file_name|
      File.extname(file_name) == '.rb'
    }.join(' ')

system("rubocop #{changed_files}") unless changed_files.empty?

exit $CHILD_STATUS.exitstatus

Make it executable

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

You're good to go, from now it'd run rubocop against your changes and prevents from commiting unless you fix the offences.

How to skip pre-commit? just pass -n to git commit

$ git commit -n -m "[hotfix] blah blah"

What is a Pre-Commit Hook?

A pre-commit hook is a client-side Git hook that runs before a commit is created. It’s a script that can do various things like run automated tests, check code style or enforce coding standards. If the pre-commit hook fails the commit is aborted and you have to fix the issues before committing again.

Why Run Rubocop Before Commit

Running Rubocop before commit has several advantages:

• Code quality: Rubocop checks code for style and security issues so the codebase is consistent and secure.
• Time saver: By running Rubocop automatically before commit you can catch issues early and avoid wasting time debugging later.
• Collaboration: By enforcing coding standards pre-commit hooks promote collaboration and consistency among team members.

How to set up a pre-commit hook

1. Install Rubocop and the pre-commit hook tool of your choice (e.g., Husky or Pre-commit).
2. Create a new file in the .git/hooks directory called pre-commit.
3. Add the Rubocop command to the pre-commit file, e.g., rubocop -a.
4. Make the pre-commit file executable by running chmod +x .git/hooks/pre-commit.
5. Test the pre-commit hook by running git commit -m “Test commit”

Note: If you want to skip the pre-commit hook temporarily you can use the –no-verify option with the git commit command, e.g., git commit -m “Test commit” –no-verify.