Essential Ruby Commands & Snippets

Ruby Basics

Running Ruby Scripts

test.rb
1ruby script.rb

Interactive Ruby Shell (IRB)

ruby snippet
1irb

ruby snippet
1irb(main):001:0> puts "Hello, Ruby!"
2Hello, Ruby!
3=> nil

Basic Syntax

ruby snippet
1# Variables
2name = "Ruby"
3age = 30
4is_awesome = true
5
6# String interpolation
7puts "Hello, #{name}!"
8
9# Conditional statements
10if age > 20
11  puts "You're over 20"
12elsif age == 20
13  puts "You're exactly 20"
14else
15  puts "You're under 20"
16end
17
18# Ternary operator
19status = is_awesome ? "Awesome" : "Not awesome"

Data Structures

Arrays

ruby snippet
1# Creating arrays
2fruits = ["apple", "banana", "orange"]
3numbers = [1, 2, 3, 4, 5]
4mixed = [1, "two", :three, 4.0]
5
6# Array operations
7fruits << "mango"           # Add to end
8fruits.push("strawberry")   # Also adds to end
9fruits.unshift("kiwi")      # Add to beginning
10fruits.pop                  # Remove from end
11fruits.shift                # Remove from beginning
12fruits[2]                   # Access by index
13fruits[-1]                  # Access last element
14fruits[1..3]                # Slice (range)

Hashes

ruby snippet
1# Creating hashes
2person = { "name" => "John", "age" => 30 }
3user = { name: "Jane", age: 25 }  # Symbol syntax
4
5# Hash operations
6person["occupation"] = "Developer"  # Add key-value pair
7user[:email] = "jane@example.com"   # Add with symbol key
8person["age"]                       # Access value
9user.keys                           # Get all keys
10user.values                         # Get all values
11user.each { |key, value| puts "#{key}: #{value}" }  # Iteration

Control Flow

Loops

ruby snippet
1# While loop
2i = 0
3while i < 5
4  puts i
5  i += 1
6end
7
8# For loop with range
9for i in 0..4
10  puts i
11end
12
13# Each iterator
14[1, 2, 3].each do |num|
15  puts num
16end
17
18# Times iterator
195.times { |i| puts i }
20
21# Until loop
22j = 0
23until j >= 5
24  puts j
25  j += 1
26end

Iterators and Blocks

ruby snippet
1# Single-line block
2[1, 2, 3].map { |n| n * 2 }  # Returns [2, 4, 6]
3
4# Multi-line block
5[1, 2, 3].each do |number|
6  squared = number * number
7  puts "#{number} squared is #{squared}"
8end
9
10# Common iterators
11[1, 2, 3, 4].select { |n| n.even? }  # Returns [2, 4]
12[1, 2, 3, 4].reject { |n| n.even? }  # Returns [1, 3]
13[1, 2, 3].reduce(0) { |sum, n| sum + n }  # Returns 6

Methods and Functions

Defining Methods

ruby snippet
1# Basic method
2def greet(name)
3  "Hello, #{name}!"
4end
5
6# Method with default parameter
7def greet_with_default(name = "World")
8  "Hello, #{name}!"
9end
10
11# Method with keyword arguments
12def introduce(name:, age:, occupation: "Developer")
13  "Meet #{name}, a #{age}-year-old #{occupation}."
14end
15
16# Calling methods
17greet("Ruby")  # "Hello, Ruby!"
18greet_with_default()  # "Hello, World!"
19introduce(name: "John", age: 30)  # "Meet John, a 30-year-old Developer."

Lambda and Proc

ruby snippet
1# Lambda
2square = ->(x) { x * x }
3square.call(5)  # Returns 25
4
5# Proc
6greeter = Proc.new { |name| puts "Hello, #{name}!" }
7greeter.call("Ruby")  # Prints "Hello, Ruby!"
8
9# Passing to methods
10def math_operation(numbers, operation)
11  numbers.map(&operation)
12end
13
14math_operation([1, 2, 3], square)  # Returns [1, 4, 9]

Object-Oriented Ruby

Classes and Objects

ruby snippet
1class Person
2  attr_accessor :name, :age
3
4  def initialize(name, age)
5    @name = name
6    @age = age
7  end
8
9  def introduce
10    "Hi, I'm #{@name} and I'm #{@age} years old."
11  end
12
13  def birthday
14    @age += 1
15    "Happy birthday! Now I'm #{@age}."
16  end
17end
18
19# Creating and using objects
20john = Person.new("John", 30)
21puts john.introduce
22puts john.birthday
23john.name = "Johnny"

Inheritance

ruby snippet
1class Animal
2  def speak
3    "Some generic animal sound"
4  end
5end
6
7class Dog < Animal
8  def speak
9    "Woof!"
10  end
11end
12
13class Cat < Animal
14  def speak
15    "Meow!"
16  end
17end
18
19fido = Dog.new
20whiskers = Cat.new
21puts fido.speak      # "Woof!"
22puts whiskers.speak  # "Meow!"

Modules and Mixins

ruby snippet
1module Flyable
2  def fly
3    "I'm flying!"
4  end
5end
6
7module Swimmable
8  def swim
9    "I'm swimming!"
10  end
11end
12
13class Bird
14  include Flyable
15end
16
17class Duck
18  include Flyable
19  include Swimmable
20end
21
22sparrow = Bird.new
23mallard = Duck.new
24puts sparrow.fly    # "I'm flying!"
25puts mallard.fly    # "I'm flying!"
26puts mallard.swim   # "I'm swimming!"

File Operations

ruby snippet
1# Reading a file
2File.open("data.txt", "r") do |file|
3  file.each_line do |line|
4    puts line
5  end
6end
7
8# Writing to a file
9File.open("output.txt", "w") do |file|
10  file.puts "Hello, Ruby!"
11  file.puts "This is a new line."
12end
13
14# Reading entire file content
15content = File.read("data.txt")
16
17# Checking if file exists
18File.exist?("data.txt")

Exception Handling

ruby snippet
1begin
2  # Code that might raise an exception
3  result = 10 / 0
4rescue ZeroDivisionError => e
5  puts "Error: #{e.message}"
6rescue => e
7  puts "Some other error occurred: #{e.message}"
8else
9  puts "No errors occurred"
10ensure
11  puts "This code always runs"
12end
13
14# Custom exceptions
15class CustomError < StandardError
16  def initialize(msg = "A custom error occurred")
17    super
18  end
19end
20
21begin
22  raise CustomError.new("Something went wrong")
23rescue CustomError => e
24  puts e.message
25end

Useful Ruby Tools

RubyGems

ruby snippet
1# Installing a gem
2gem install nokogiri
3
4# Listing installed gems
5gem list
6
7# Updating a gem
8gem update rails
9
10# Uninstalling a gem
11gem uninstall nokogiri

Bundler

ruby snippet
1# Installing bundler
2gem install bundler
3
4# Installing gems from Gemfile
5bundle install
6
7# Updating gems
8bundle update
9
10# Running a command in the context of the bundle
11bundle exec rspec

Regular Expressions

ruby snippet
1# Basic pattern matching
2"hello" =~ /ello/  # Returns 1 (index of match)
3
4# Pattern with modifiers
5"Hello World" =~ /hello/i  # Case-insensitive match
6
7# String methods with regex
8"hello".gsub(/[aeiou]/, '*')  # "h*ll*"
9"hello world".scan(/\w+/)     # ["hello", "world"]
10
11# Matching groups
12match_data = "John Smith".match(/(\w+) (\w+)/)
13first_name = match_data[1]  # "John"
14last_name = match_data[2]   # "Smith"