Ruby Gems and Bundler

## Learning Objectives - Understand RubyGems structure - Use gem command line tool - Manage dependencies with Bundler - Create and distribute gems ## RubyGems Overview RubyGems is Ruby's package manager. Gems are reusable libraries distributed as packages. ### Finding Gems ```bash gem search rails # Search for gems gem list # List installed gems gem info rails # Show gem info ``` ### Installing Gems ```bash gem install gem_name gem install gem_name --version '~> 2.0' gem install rails --no-document # Skip documentation ``` ### Using Installed Gems ```ruby require 'gem_name' # Or specify version gem 'rake', '~> 13.0' require 'rake' ``` ## Bundler Bundler manages gem dependencies for Ruby projects. ### Gemfile Create a `Gemfile` in your project root: ```ruby source 'https://rubygems.org' # Specify gem with version gem 'rails', '~> 7.0' # Gem without version (uses latest) gem 'puma' # Gem with options gem 'mysql2', '>= 0.4.4', '< 1.0' # Git repository gem 'capistrano', git: 'https://github.com/capistrano/capistrano.git' # Local path gem 'my gem', path: '~/code/my_gem' # Groups group :development, :test do gem 'rspec' gem 'pry' end ``` ### Install Dependencies ```bash bundle install bundle install --jobs=4 # Parallel installation bundle update # Update all gems ``` ### Gemfile.lock After `bundle install`, `Gemfile.lock` is created with exact versions: ```ruby GEM remote: https://rubygems.org/ specs: rails (7.0.0) actionmailbox (= 7.0.0) ... rspec (3.10.0) ... PLATFORMS ruby DEPENDENCIES rails (~> 7.0) rspec BUNDLED WITH 2.3.0 ``` ### Using Gems in Code ```ruby require 'bundler/setup' # Or let Bundler setup automatically require 'bundler' Bundler.require # In a script require 'bundler/setup' ``` ### Running Gems ```bash bundle exec rspec bundle exec rake db:migrate bundle exec ruby script.rb ``` ## Bundler Commands ```bash bundle install # Install dependencies bundle update # Update gems bundle exec CMD # Run command in bundle context bundle list # List installed gems bundle show GEM # Show gem path bundle check # Verify dependencies bundle outdated # Check for outdated gems bundle init # Create new Gemfile ``` ## Creating a Gem ### Structure ```text my_gem/ ├── my_gem.gemspec ├── lib/ │ └── my_gem/ │ ├── version.rb │ └── my_gem.rb ├── spec/ │ └── my_gem_spec.rb └── README.md ``` ### Gemspec File ```ruby Gem::Specification.new do |s| s.name = 'my_gem' s.version = '1.0.0' s.authors = ['Your Name'] s.email = 'your@email.com' s.summary = 'A sample gem' s.description = 'A longer description' s.homepage = 'https://github.com/you/my_gem' s.license = 'MIT' s.files = `git ls-files -z`.split("\x0") s.require_paths = ['lib'] s.required_ruby_version = '>= 2.4' s.add_dependency 'json' s.add_development_dependency 'rspec', '~> 3.0' end ``` ### Main Library File ```ruby # lib/my_gem.rb require 'my_gem/version' module MyGem class Error < StandardError; end def self.greet(name) "Hello, #{name}!" end end ``` ```ruby # lib/my_gem/version.rb module MyGem VERSION = '1.0.0' end ``` ### Build and Install ```bash gem build my_gem.gemspec gem install ./my_gem-1.0.0.gem gem push my_gem-1.0.0.gem # Publish to RubyGems.org ``` ## Common Gems ### Web Frameworks | Gem | Description | |-----|-------------| | rails | Full-stack web framework | | sinatra | Lightweight web framework | | rack | Web server interface | ### Database | Gem | Description | |-----|-------------| | activerecord | ORM (part of Rails) | | sequel | Lightweight ORM | | pg | PostgreSQL adapter | ### Testing | Gem | Description | |-----|-------------| | rspec | BDD testing framework | | minitest | Unit testing framework | | capybara | Integration testing | | factory_bot | Test fixtures | ### Utilities | Gem | Description | |-----|-------------| | pry | REPL and debugger | | bundler | Dependency manager | | rake | Task automation | | faraday | HTTP client | ## .gemspec vs Gemfile | Aspect | gemspec | Gemfile | |--------|---------|---------| | Purpose | Package definition | Dependency management | | Used by | gem build/install | bundle install | | Versioning | In file | Lock file | | Platform | gem install | bundle exec | ## Summary - RubyGems is the package manager for Ruby - `gem install` installs globally - Bundler manages project dependencies via Gemfile - `bundle install` installs from Gemfile - `bundle exec` runs commands in bundle context - Gemspec defines gem metadata and dependencies - `gem build` and `gem push` for publishing