Ruby Gems and Bundler

Master Ruby's package management system with gems and Bundler. Learn to manage dependencies, create gems, and publish to RubyGems.

Bundler Basics

Gemfile

source 'https://rubygems.org'

# Ruby version
ruby '3.3.0'

# Production gems
gem 'rails', '~> 7.1'
gem 'pg', '>= 1.1'
gem 'puma', '~> 6.0'

# Development and test gems
group :development, :test do
  gem 'rspec-rails'
  gem 'factory_bot_rails'
  gem 'faker'
end

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

# Test only
group :test do
  gem 'capybara'
  gem 'selenium-webdriver'
end

# Git source
gem 'my_gem', git: 'https://github.com/user/my_gem.git'

# Local path (for development)
gem 'local_gem', path: '../local_gem'

# Specific branch
gem 'experimental_gem', git: 'https://github.com/user/repo.git', branch: 'develop'

# Require specific file or false to not auto-require
gem 'sidekiq', require: 'sidekiq/web'
gem 'bootsnap', require: false

Version Constraints

# Exact version
gem 'rails', '7.1.0'

# Pessimistic operator (allows patch updates)
gem 'rails', '~> 7.1.0'  # >= 7.1.0 and < 7.2.0
gem 'rails', '~> 7.1'    # >= 7.1.0 and < 8.0.0

# Greater than or equal
gem 'pg', '>= 1.1'

# Range
gem 'ruby-version', '>= 1.0', '< 2.0'

# Multiple constraints
gem 'nokogiri', '>= 1.10', '< 2.0'

Bundler Commands

# Install all gems from Gemfile
bundle install

# Install to specific path
bundle install --path vendor/bundle

# Update all gems
bundle update

# Update specific gem
bundle update rails

# Check for outdated gems
bundle outdated

# Show gem location
bundle show rails

# Execute command with bundled gems
bundle exec rspec

# Open gem in editor
bundle open rails

# Check Gemfile syntax
bundle check

# Remove unused gems
bundle clean

# List all installed gems
bundle list

# Show dependency tree
bundle viz

Gemfile.lock

The Gemfile.lock file locks gem versions for consistent installations:

# Always commit Gemfile.lock to version control
# This ensures all developers use same gem versions

# Regenerate Gemfile.lock
rm Gemfile.lock
bundle install

Creating Gems

Gem Structure

# Create new gem
bundle gem my_gem

# Structure:
my_gem/
├── lib/
│   ├── my_gem/
│   │   └── version.rb
│   └── my_gem.rb
├── spec/
│   ├── my_gem_spec.rb
│   └── spec_helper.rb
├── bin/
│   ├── console
│   └── setup
├── .gitignore
├── Gemfile
├── LICENSE.txt
├── my_gem.gemspec
├── Rakefile
└── README.md

Gemspec

# my_gem.gemspec
require_relative 'lib/my_gem/version'

Gem::Specification.new do |spec|
  spec.name          = "my_gem"
  spec.version       = MyGem::VERSION
  spec.authors       = ["Your Name"]
  spec.email         = ["your.email@example.com"]

  spec.summary       = "Short summary of gem"
  spec.description   = "Longer description of what gem does"
  spec.homepage      = "https://github.com/username/my_gem"
  spec.license       = "MIT"

  spec.required_ruby_version = ">= 3.0.0"

  spec.metadata["homepage_uri"] = spec.homepage
  spec.metadata["source_code_uri"] = "https://github.com/username/my_gem"
  spec.metadata["changelog_uri"] = "https://github.com/username/my_gem/CHANGELOG.md"

  # Specify which files should be added to the gem
  spec.files = Dir.chdir(File.expand_path(__dir__)) do
    `git ls-files -z`.split("\x0").reject do |f|
      f.match(%r{\A(?:test|spec|features)/})
    end
  end

  spec.bindir        = "exe"
  spec.executables   = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
  spec.require_paths = ["lib"]

  # Runtime dependencies
  spec.add_dependency "activesupport", "~> 7.0"
  spec.add_dependency "nokogiri", ">= 1.10"

  # Development dependencies
  spec.add_development_dependency "rspec", "~> 3.12"
  spec.add_development_dependency "rubocop", "~> 1.50"
end

Version File

# lib/my_gem/version.rb
module MyGem
  VERSION = "0.1.0"
end

Main Library File

# lib/my_gem.rb
require_relative "my_gem/version"
require_relative "my_gem/core"
require_relative "my_gem/helpers"

module MyGem
  class Error < StandardError; end

  def self.configure
    yield configuration
  end

  def self.configuration
    @configuration ||= Configuration.new
  end

  class Configuration
    attr_accessor :api_key, :timeout

    def initialize
      @api_key = nil
      @timeout = 30
    end
  end
end

Building and Publishing

Build Gem

# Build gem locally
gem build my_gem.gemspec

# This creates my_gem-0.1.0.gem

# Install locally for testing
gem install ./my_gem-0.1.0.gem

# Uninstall
gem uninstall my_gem

Publish to RubyGems

# First time setup (one-time)
gem push my_gem-0.1.0.gem
# You'll be prompted to log in

# For subsequent pushes
gem push my_gem-0.2.0.gem

# Yank a version (removes from RubyGems)
gem yank my_gem -v 0.1.0

# Unyank a version
gem unyank my_gem -v 0.1.0

Versioning

# Semantic Versioning: MAJOR.MINOR.PATCH
# 1.0.0 -> 1.0.1 (patch)
# 1.0.1 -> 1.1.0 (minor)
# 1.1.0 -> 2.0.0 (major)

# lib/my_gem/version.rb
module MyGem
  VERSION = "1.0.0"
end

# Update version, then build and push:
# 1. Edit version.rb
# 2. gem build my_gem.gemspec
# 3. gem push my_gem-1.0.0.gem

RubyGems Commands

# List installed gems
gem list

# Search for gems
gem search rails

# Show gem info
gem info rails

# List gem dependencies
gem dependency rails

# Update all gems
gem update

# Update specific gem
gem update rails

# Cleanup old versions
gem cleanup

# Show gem environment
gem env

# Install specific version
gem install rails -v 7.1.0

# Install without documentation (faster)
gem install rails --no-document

# Uninstall gem
gem uninstall rails

# Fetch gem but don't install
gem fetch rails

Gem Groups

# Define groups
group :development do
  gem 'pry'
end

group :test do
  gem 'rspec'
end

group :development, :test do
  gem 'factory_bot'
end

# Install without specific groups
bundle install --without production

# Require specific groups
Bundler.require(:default, :development)

Gem Sources

# Primary source
source 'https://rubygems.org'

# Additional sources
source 'https://gems.example.com' do
  gem 'private_gem'
end

# Git sources
gem 'my_gem', git: 'https://github.com/user/my_gem.git'
gem 'my_gem', git: 'https://github.com/user/my_gem.git', tag: 'v1.0'
gem 'my_gem', git: 'https://github.com/user/my_gem.git', branch: 'main'
gem 'my_gem', git: 'https://github.com/user/my_gem.git', ref: 'abc123'

# GitHub shorthand
gem 'my_gem', github: 'user/my_gem'

# Local path
gem 'my_gem', path: '../my_gem'

Requiring Gems

# In code
require 'my_gem'

# Bundler auto-requires gems based on Gemfile
# To disable auto-require:
gem 'my_gem', require: false

# Then manually require where needed:
require 'my_gem'

# Require specific file
gem 'sidekiq', require: 'sidekiq/web'

Platform-Specific Gems

# Only install on specific platforms
gem 'pg', platforms: :ruby
gem 'sqlite3', platforms: [:mingw, :mswin, :x64_mingw]

# Multiple platforms
platforms :ruby do
  gem 'pg'
  gem 'nokogiri'
end

platforms :jruby do
  gem 'activerecord-jdbc-adapter'
end

Private Gems

Using Private Gem Server

# Gemfile
source 'https://rubygems.org'

source 'https://gems.mycompany.com' do
  gem 'private_gem'
end

Using Git Credentials

# .netrc file for private repos
machine github.com
  login your-username
  password your-token

Gem Development

Using bundle console

# Open IRB with gem loaded
bin/console

# Or
bundle console

Running Tests

# Using Rake
rake spec

# Or directly
bundle exec rspec

Local Development

# In your app's Gemfile, point to local gem
gem 'my_gem', path: '../my_gem'

# Or use bundle config
bundle config local.my_gem ../my_gem

Best Practices

1. Always commit Gemfile.lock to version control
2. Use pessimistic versioning (~>) for stability
3. Keep gems updated but test thoroughly
4. Use groups to separate dev/test/production gems
5. Specify Ruby version in Gemfile for consistency
6. Use bundle exec to ensure correct gem versions
7. Document gem dependencies and why they're needed
8. Test gems locally before publishing
9. Follow semantic versioning for your gems
10. Keep gemspecs clean and well-documented

Anti-Patterns

❌ Don't commit vendor/bundle to git (use .gitignore) ❌ Don't use require: false unnecessarily - adds manual work ❌ Don't specify exact versions unless absolutely necessary ❌ Don't push untested gem versions to RubyGems ❌ Don't include unnecessary files in gem packages ❌ Don't hardcode credentials in gemspec or Gemfile

Troubleshooting

# Clear bundler cache
bundle clean --force

# Regenerate Gemfile.lock
rm Gemfile.lock && bundle install

# Check for gem conflicts
bundle exec gem dependency

# Verbose output
bundle install --verbose

# Show why a gem is needed
bundle show rails

# List all gem versions
bundle list

Related Skills

• ruby-oop - For structuring gem code
• ruby-metaprogramming - Used in many gems
• ruby-standard-library - Core Ruby functionality