Git hook for Rails projects that ensures dependencies are up-to-date and reminds devs to run pending migrations after switching branches

post-checkout

#!/usr/bin/env bash

set -euo pipefail

# Exit during rebases, merges, or detached HEADs
if [ -d .git/rebase-merge ] || [ -d .git/rebase-apply ] || [ -f .git/MERGE_HEAD ] || ! git symbolic-ref -q HEAD >/dev/null; then
  echo "🔁 Skipping post-checkout hook (rebase/merge or detached HEAD)"
  exit 0
fi

previous_head=$(git rev-parse HEAD@{1})
new_head=$(git rev-parse HEAD)

# Check for Gemfile.lock changes
if git diff --name-only "$previous_head" "$new_head" | grep -q '^Gemfile.lock$'; then
  echo "📦 Gemfile.lock changed. Running bundle install..."
  if ! bundle install; then
    echo "❌ bundle install failed!" >&2
    exit 1
  fi
fi

# Warn if new migrations were added
if git diff --name-only "$previous_head" "$new_head" | grep -q '^db/migrate/'; then
  echo "🛠️  New migration(s) detected. Don't forget to run:"
  echo "    rails db:migrate"
fi

💡 A post-checkout Git hook for Ruby on Rails projects

This hook ensures you’re running the right dependencies and don’t forget pending migrations after switching branches.

Features

• ✅ Runs bundle install when Gemfile.lock changes
• ✅ Warns you if new files are added to db/migrate
• ✅ Skips during rebases, merges, or detached HEAD states

Installation

1. Save the script as .git/hooks/post-checkout in your Rails project.

2. Make it executable:

   chmod +x .git/hooks/post-checkout

Now every time you checkout a branch, this hook will help keep your environment in sync.