Ruby Cheat Sheet

Ruby syntax, blocks, symbols, mixins, and enumerable methods for expressive, object-oriented scripting and web development.

2 PagesBeginnerMar 25, 2026

Basic Syntax

Variables, control flow, and iteration.

ruby

age = 30name = "Ada"pi = 3.14159is_fun = trueif age >= 18  puts "#{name} is an adult"end5.times do |i|  puts "Count: #{i}"end

Blocks & Iterators

Enumerable methods with blocks.

ruby

nums = [5, 3, 1, 4, 2]nums.each { |n| puts n }evens = nums.select { |n| n.even? }   # [4, 2]squared = nums.map { |n| n * n }      # [25, 9, 1, 16, 4]sum = nums.reduce(0) { |acc, n| acc + n }  # 15sorted = nums.sort                    # [1, 2, 3, 4, 5]

Core Enumerable Methods

Frequently used methods on collections.

.each- iterates over a collection without returning a new one
.map- transforms each element, returns a new array
.select / .reject- filters elements by a block's truthiness
.reduce (inject)- accumulates a single value across elements
.nil? / .empty?- checks for nil or an empty collection/string
.to_s / .to_i- converts an object to a String/Integer
attr_accessor- generates getter and setter methods for instance variables

Classes & Mixins

Object-oriented Ruby with modules.

ruby

module Greetable  def greet    "Hello, #{name}"  endendclass Person  include Greetable  attr_accessor :name, :age  def initialize(name, age)    @name = name    @age = age  endendp = Person.new("Ada", 30)puts p.greet   # "Hello, Ada"

Pro Tip

Use `Symbol` (:name) instead of `String` for hash keys and identifiers — symbols are immutable and reused, making comparisons faster than string equality checks.

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