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Ruby Programming Language Cheatsheet

A comprehensive cheat sheet covering essential Ruby syntax, data structures, control flow, and object-oriented programming concepts.

Ruby Basics

Syntax

Comments

# This is a single-line comment

=begin
This is a multi-line comment
=end

Variables

variable_name = value (snake_case)

Constants

CONSTANT_NAME = value (UPPER_SNAKE_CASE)

String Interpolation

"Hello, #{variable_name}!"

Blocks

do ... end or { ... }

Methods

 
def method_name(arg1, arg2)
  # method body
  return value
end

Data Types

Numbers: Integers (1, 2, 3), Floats (1.0, 2.5), Rational (1/2)

Strings: "Hello, world!", 'Single quotes'

Booleans: true, false

Symbols: :symbol_name (immutable strings)

Arrays: [1, 2, "three"]

Hashes: { :key1 => "value1", "key2" => 2 }

Nil: nil (represents absence of value)

Operators

Arithmetic

+, -, *, /, %, ** (exponentiation)

Comparison

==, !=, >, <, >=, <=, <=>

Logical

&& (and), || (or), ! (not)

Assignment

=, +=, -=, *=, /=, %=, **=

Control Flow

Conditional Statements

If Statement

if condition
  # code to execute if true
elsif other_condition
  # code to execute if other_condition is true
else
  # code to execute if false
end

Unless Statement

unless condition
  # code to execute if condition is false
else
  # code to execute if condition is true
end

Ternary Operator

condition ? true_value : false_value

Case Statement

case variable
when value1
  # code to execute if variable == value1
when value2
  # code to execute if variable == value2
else
  # code to execute if no other value matches
end

Loops

While Loop

while condition
  # code to execute while true
end

Until Loop

until condition
  # code to execute until true
end

For Loop

for variable in collection
  # code to execute for each element
end

Each Iterator (Array/Hash)

array.each do |element|
  # code to execute for each element
end

hash.each do |key, value|
  # code to execute for each key-value pair
end

Loop Control
break - exits the loop.
next - skips the current iteration.

Exception Handling 

begin
  # code that might raise an exception
rescue SpecificError => e
  # code to handle specific exception
rescue => e
  # code to handle other exceptions
ensure
  # code that always executes (optional)
end

Object-Oriented Programming

Classes and Objects

Class Definition

class ClassName
  # attributes and methods
end

Creating Objects

object = ClassName.new

Attributes (Instance Variables)

class ClassName
  attr_accessor :attribute1, :attribute2  # getter and setter
  attr_reader :attribute3  # getter only
  attr_writer :attribute4  # setter only
end

Instance Methods

class ClassName
  def method_name(arg1, arg2)
    # method body
  end
end

Class Methods

class ClassName
  def self.method_name
    # method body
  end
end

Constructor (initialize method)

class ClassName
  def initialize(arg1, arg2)
    @attribute1 = arg1
    @attribute2 = arg2
  end
end

Inheritance

Inheriting from a Class

class SubClass < SuperClass
  # override methods or add new ones
end

Calling Superclass Methods

def method_name(arg1, arg2)
  super(arg1, arg2)
  # additional code
end

Modules

Module Definition

module ModuleName
  # constants and methods
end

Including Modules

class ClassName
  include ModuleName
end

Extending Modules

class ClassName
  extend ModuleName
end

Using Modules as Namespaces

ModuleName::CONSTANT
ModuleName.method_name

Common Methods

String Methods

length

Returns the length of the string.

upcase

Converts the string to uppercase.

downcase

Converts the string to lowercase.

strip

Removes leading and trailing whitespace.

split(delimiter)

Splits the string into an array based on the delimiter.

include?(substring)

Checks if the string contains the substring.

Array Methods

length or size

Returns the number of elements in the array.

push(element) or << element

Adds an element to the end of the array.

pop

Removes and returns the last element of the array.

shift

Removes and returns the first element of the array.

unshift(element)

Adds an element to the beginning of the array.

include?(element)

Checks if the array contains the element.

Hash Methods

length or size

Returns the number of key-value pairs in the hash.

keys

Returns an array of all keys in the hash.

values

Returns an array of all values in the hash.

has_key?(key)

Checks if the hash contains the key.

has_value?(value)

Checks if the hash contains the value.

delete(key)

Deletes the key-value pair from the hash.
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