Ruby: Standard Library, Gems & Tooling

Standard Library Highlights

require 'json'
JSON.parse('{"name": "Alice"}')  # => {"name" => "Alice"}
{ name: "Alice" }.to_json        # => '{"name":"Alice"}'

require 'date'
Date.today                        # #<Date: 2026-05-07>
Date.parse("2026-01-15")
DateTime.now
Time.now.strftime("%Y-%m-%d %H:%M")

require 'net/http'
require 'uri'
uri = URI('https://api.example.com/users')
response = Net::HTTP.get_response(uri)
JSON.parse(response.body)

require 'fileutils'
FileUtils.mkdir_p('path/to/dir')
FileUtils.cp('src.txt', 'dst.txt')
FileUtils.rm_rf('temp/')

require 'erb'
template = ERB.new("Hello, <%= name %>!")
template.result(binding)   # "Hello, Alice!" (uses local binding)

require 'digest'
Digest::SHA256.hexdigest("password")
Digest::MD5.hexdigest("data")

Gems & Bundler

# Gemfile
source "https://rubygems.org"
ruby "3.3.0"

gem "rails", "~> 7.2"          # ~> means >= 7.2, < 8.0
gem "pg"                        # PostgreSQL adapter
gem "puma"                      # Web server
gem "sidekiq"                   # Background jobs

group :development, :test do
  gem "rspec-rails"
  gem "factory_bot_rails"
end

group :test do
  gem "faker"
  gem "shoulda-matchers"
end

# Bundler commands
bundle install          # install gems from Gemfile
bundle update rails     # update specific gem
bundle exec rspec       # run command in bundle context
bundle exec rake db:migrate

gem install bundler     # install bundler itself
gem list                # list installed gems

RSpec Testing

# spec/models/user_spec.rb
require 'rails_helper'

RSpec.describe User, type: :model do
  let(:user) { build(:user) }             # FactoryBot

  describe 'validations' do
    it { is_expected.to validate_presence_of(:email) }
    it { is_expected.to validate_uniqueness_of(:email) }
  end

  describe '#full_name' do
    it 'combines first and last name' do
      user = described_class.new(first_name: 'Alice', last_name: 'Smith')
      expect(user.full_name).to eq('Alice Smith')
    end
  end

  context 'when admin' do
    let(:admin) { create(:user, :admin) }

    it 'can access admin panel' do
      expect(admin.can?(:access, :admin_panel)).to be true
    end
  end
end

Version Management & Tooling

# rbenv (recommended version manager)
rbenv install 3.3.2
rbenv global 3.3.2
rbenv local 3.2.0      # .ruby-version in project dir

# RVM (alternative)
rvm install 3.3.2
rvm use 3.3.2 --default

# Common tools
gem install solargraph    # LSP for IDE support
gem install rubocop       # linter/formatter
gem install brakeman      # security scanner
gem install pry           # better REPL than irb

# Interactive Ruby
irb                       # built-in REPL
pry                       # enhanced REPL with debugging

# Rake tasks
rake -T                   # list all tasks
rake db:migrate
rake test