Ruby Cheat Sheet

puts "Hello, World!"

# Single line comment
=begin
Multi-line
comment
=end

print "Name: "
name = gets.chomp

"42".to_i   # string to int
42.to_s     # int to string
"3.14".to_f # to float

variable.class      # String, Integer
variable.is_a?(String)  # true/false

name = "John"

age = 25

price = 19.99

fruits = ["apple", "banana", "cherry"]

person = { name: "John", age: 30 }

:status

(1..5)  # 1 to 5 inclusive
(1...5) # 1 to 4

5 + 3   # 8 (addition)
5 - 3   # 2 (subtraction)
5 * 3   # 15 (multiplication)
5 / 3   # 1 (integer division)
5.0 / 3 # 1.666... (float division)
5 % 3   # 2 (modulus)
5 ** 3  # 125 (exponent)

5 == 5  # true (equal)
5 != 3  # true (not equal)
5 > 3   # true (greater)
5 <=> 3 # 1 (spaceship: -1, 0, 1)
5.eql?(5)   # true (same type)

true && false   # false (AND)
true || false   # true (OR)
!true           # false (NOT)
true and false  # false (lower precedence)
true or false   # true (lower precedence)

x = 5     # Assign
x += 3    # x = 8 (add)
x -= 2    # x = 6 (subtract)
x *= 2    # x = 12 (multiply)
x ||= 10  # x = 12 (assign if nil/false)

(1..5)   # 1, 2, 3, 4, 5 (inclusive)
(1...5)  # 1, 2, 3, 4 (exclusive)
('a'..'e').to_a  # ["a", "b", "c", "d", "e"]

user&.name       # nil if user is nil
user&.profile&.email  # safe chain

(1..5).each do |i|
  puts i
end

[1, 2, 3].each { |n| puts n }

5.times { |i| puts i }  # 0, 1, 2, 3, 4

1.upto(5) { |i| puts i }
5.downto(1) { |i| puts i }

while count < 10
  count += 1
end

until count >= 10
  count += 1
end

loop do
  break if done
end

arr.each_with_index do |item, i|
  puts "#{i}: #{item}"
end

(1..10).each do |i|
  next if i == 5   # skip
  break if i == 8  # exit
  puts i
end

if x > 0
  puts "positive"
elsif x < 0
  puts "negative"
else
  puts "zero"
end

puts "active" unless inactive

result = condition ? "yes" : "no"

case day
when "Mon"
  puts "Monday"
when "Tue", "Wed"
  puts "Midweek"
else
  puts "Other"
end

puts "big" if x > 100

def greet(name)
  "Hello, #{name}!"
end

def greet(name = "World")
  "Hello, #{name}!"
end

def sum(*nums)
  nums.reduce(0, :+)
end

def greet(name:, age: 0)
  "#{name} is #{age}"
end

def with_timing
  start = Time.now
  yield
  Time.now - start
end

[1, 2, 3].map { |n| n * 2 }

[1, 2, 3, 4].select { |n| n.even? }

[1, 2, 3, 4].reject { |n| n.even? }

[1, 2, 3].reduce(0) { |sum, n| sum + n }

users.find { |u| u.id == 1 }

[3, 1, 2].sort
users.sort_by { |u| u.age }

class Dog
  attr_accessor :name

  def initialize(name)
    @name = name
  end

  def bark
    "#{@name} says woof!"
  end
end

class Puppy < Dog
  def play
    "#{@name} is playing!"
  end
end

module Greetable
  def greet
    "Hello!"
  end
end

class Person
  include Greetable
end

"Hello, #{name}!"

"Hello" + " " + "World"

"a,b,c".split(",")

["a", "b", "c"].join(",")

"  hello  ".strip

"hello".gsub("l", "x")

begin
  risky_operation
rescue StandardError => e
  puts e.message
end

begin
  # code
rescue
  # handle
ensure
  cleanup
end

raise ArgumentError, "Invalid input"