Bundler

Bundler is a Ruby gem dependency manager that ensures consistent gem versions across development, testing, and production environments.

Installation

# Install bundler gem globally
gem install bundler

# Check version
bundle --version

# Update bundler
gem update bundler

Gemfile Management

Basic Gemfile

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '3.2.0'

# Core gems
gem 'rails', '~> 7.0.0'
gem 'sqlite3', '~> 1.4'
gem 'puma', '~> 5.0'
gem 'sass-rails', '~> 6'
gem 'webpacker', '~> 5.0'

# Database
gem 'pg', '~> 1.1'
gem 'redis', '~> 4.0'

# Development gems
group :development do
  gem 'web-console', '>= 4.1.0'
  gem 'rack-mini-profiler', '~> 2.0'
  gem 'byebug', platforms: [:mri, :mingw]
end

# Test gems
group :test do
  gem 'rspec-rails'
  gem 'factory_bot_rails'
  gem 'capybara'
end

Essential Commands

# Install dependencies
bundle install

# Install without development/test gems
bundle install --without development test

# Install in vendor/bundle
bundle install --path vendor/bundle

# Update all gems
bundle update

# Update specific gem
bundle update rails

# List installed gems
bundle list

# Show gem information
bundle show rails
bundle show --paths

# Verify gemfile
bundle check

# Execute command in bundle context
bundle exec rspec

# Generate Gemfile.lock
bundle lock

Gem Version Constraints

|Operator|Example|Meaning| |---------|-------------| |=|gem 'rails', '= 7.0.0'|Exact version| |~>|gem 'rails', '~> 7.0'|Pessimistic (7.0.x)| |>=|gem 'rails', '>= 7.0.0'|Greater or equal| |>|gem 'rails', '> 7.0.0'|Greater than| |<=|gem 'rails', '<= 7.0.0'|Less or equal| |<|gem 'rails', '< 7.0.0'|Less than|

Grouping Gems

# Development only
group :development do
  gem 'rails-erd'
  gem 'annotate'
end

# Testing only
group :test do
  gem 'rspec-rails'
  gem 'factory_bot_rails'
end

# Development and test
group :development, :test do
  gem 'pry-rails'
  gem 'dotenv-rails'
end

# Production only
group :production do
  gem 'pg'
  gem 'rails_12factor'
end

Gemfile.lock

# Lock specific versions
bundle lock

# Update with new compatible versions
bundle lock --update

# Update specific gem
bundle lock --update rails

# Remove lock file
rm Gemfile.lock

# Regenerate
bundle install

Common Workflows

New Rails Project

# Create new Rails app
rails new myapp
cd myapp

# Install gems
bundle install

# Generate scaffold
bundle exec rails generate scaffold Post title:string content:text
bundle exec rails db:migrate

Adding New Gem

# Add to Gemfile
echo "gem 'devise'" >> Gemfile

# Install
bundle install

# Or use bundle add
bundle add devise

Updating Gems

# Update all gems
bundle update

# Show outdated gems
bundle outdated

# Update specific gem
bundle update rails

# Clean up unused gems
bundle clean

Bundler Configuration

.bundle/config

---
BUNDLE_PATH: vendor/bundle
BUNDLE_JOBS: 4
BUNDLE_RETRY: 3

Command Line Config

# Set path
bundle config set --local path 'vendor/bundle'

# Set jobs
bundle config set jobs 4

# Unset config
bundle config unset path

Troubleshooting

# Clear bundler cache
bundle clean --force

# Rebuild gems
bundle install --redownload

# Check for conflicts
bundle check

# Install missing gems
bundle install --missing

# Verbose output
bundle install --verbose

# Update gems to latest compatible
bundle update

Docker Integration

Dockerfile

FROM ruby:3.2

WORKDIR /app

# Install dependencies
RUN apt-get update && apt-get install -y postgresql-client

# Copy Gemfile
COPY Gemfile Gemfile.lock ./

# Install gems
RUN bundle install --jobs 4 --retry 3

COPY . .

CMD ["rails", "server", "-b", "0.0.0.0"]

CI/CD Integration

GitHub Actions

name: Tests
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: ruby/setup-ruby@v1
        with:
          ruby-version: 3.2
          bundler-cache: true
      - run: bundle exec rspec

Best Practices

Always commit Gemfile.lock to version control
Use pessimistic version constraints (~>) for stability
Review Gemfile regularly for security updates
Run bundle audit to check for vulnerabilities
Use separate Gemfiles for different environments if needed
Keep gems updated with bundle outdated
Use bundle clean to remove unused gems

Resources

Last updated: 2025-07-06|Edit on GitHub