Get Started

# ===== 1. Install Ruby (version manager) =====
# rbenv (macOS / Linux):
brew install rbenv ruby-build
rbenv init
rbenv install 3.3.0
rbenv global 3.3.0

# asdf (cross-language):
asdf plugin add ruby
asdf install ruby 3.3.0
asdf global ruby 3.3.0

# Windows: RubyInstaller from rubyinstaller.org

ruby --version
gem --version

# ===== 2. Hello, Ruby =====
# hello.rb
puts 'hello, Ruby'

ruby hello.rb

# ===== 3. Bundler =====
gem install bundler
bundle init       # creates Gemfile

# Gemfile
source 'https://rubygems.org'
gem 'sinatra'
gem 'rspec', group: :test

bundle install

# ===== 4. A tiny Sinatra app =====
# app.rb
require 'sinatra'

get '/healthz' do
  content_type :json
  '{"ok":true}'
end

bundle exec ruby app.rb
# Visit http://localhost:4567/healthz

# ===== 5. Tests (RSpec) =====
bundle exec rspec --init

# spec/calc_spec.rb
RSpec.describe 'arithmetic' do
  it 'adds' do
    expect(1 + 1).to eq(2)
  end
end

bundle exec rspec

# ===== 6. Rails (when you want it) =====
gem install rails
rails new shop
cd shop
bin/rails generate scaffold Product name:string price:decimal
bin/rails db:migrate
bin/rails server
# In 30 seconds you have working CRUD.

# ===== 7. Project layout (small lib) =====
# Gemfile
# lib/
# spec/
# bin/

# ===== Patterns to internalise =====
# - Always pin Ruby with .ruby-version + bundler
# - Use bundle exec to avoid PATH surprises
# - RSpec or Minitest; pick one per project
# - frozen_string_literal: true at the top of every file

# ===== Pitfalls =====
# - sudo gem install -> breaks rbenv shims; use bundler instead
# - Running 'ruby foo.rb' when 'bundle exec ruby foo.rb' is needed
# - Mixing global gems with project Gemfile
# - Forgetting to commit Gemfile.lock for apps (commit it for apps; libraries may skip)

# install via rbenv / asdf / Homebrew
ruby -v
ruby hello.rb