Learn Ruby in X Minutes

Ruby is a dynamic, open source programming language with a focus on simplicity and productivity. It has an elegant syntax that is natural to read and easy to write.

Installation

Ruby can be installed on many platforms (Linux, Mac, Windows and etc.). Here not lists how to install it.

Please refer to https://www.ruby-lang.org/en/downloads/ to install ruby on the platform you use.

If you are using Linux or Mac, I recommend you to install ruby through RVM (Ruby Version Manager).

"RVM is a command-line tool which allows you to easily install, manage, and work with multiple ruby environments from interpreters to sets of gems."

Install RVM with a Ruby:

$ \curl -sSL https://get.rvm.io | bash -s stable

Magic

$ irb
> name="world"
=> "world"
> puts "Hello #{name}"
Hello world
=> nil

Input and Output

> name=gets
Jeoygin
=> "Jeoygin\n"
> puts "Hello #{name}"
Jeoygin
=> nil
> puts 'Hello world'
Hello world
=> nil
> print 'Hello world'
Hello world=> nil
> profession=$stdin.gets
Engineer
=> "Engineer\n"
> $stdout.puts "I'm #{profession}"
I'm Engineer
=> nil
> $stderr.puts "This is error info"
This is error info
=> nil
> inp = $stdin.read
First line
Second line
Third line
Last line
Ctrl+D
=> "First line\nSecond line\nThird line\nLast line\n"
> ios = IO.new STDOUT.fileno
=> #<IO:fd 1>
> ios.write "Jeoygin\n"
Jeoygin
=> 8
> ios.close
=> nil

puts append "\n" at the end automatically.

redirect.rb

#!/usr/bin/ruby

$stdout = File.open "output.log", "a"

puts "Ruby"
puts "Java"

$stdout.close
$stdout = STDOUT

puts "Python"

Useful Methods

> 8.class
=> Fixnum
> Fixnum.superclass
=> Integer
> "Hello".length
=> 5
> "Hello".index("l")
=> 2
> nil.nil?
=> true
> 8.methods
=> [:to_s, :inspect, :-@, :+, :-, :*, :/, :div, :%, :modulo, ...
 :nil?, :=~, :protected_methods, :private_methods, :public_methods, 
 :instance_variables, :instance_of?, :is_a?, :equal?, :object_id, ...
 ]

Control Structures

Condition

> x = 4
> if x > 10
    puts "Greater than 10"
  elsif x < 0
    puts "Less than 0"
  else
    puts "1..10"
  end
1..10
=> nil
> puts 'This appears to be true.' if x == 4
This appears to be true.
=> nil
> puts 'This appears to be false.' unless x == 4
=> nil
> unless x == 4
    puts 'This appears to be false.'
  else
    puts 'This appears to be true.'
  end
This appears to be true.
=> nil

Loop

> x = 0
> x = x + 1 while x < 10
=> nil
> x
=> 10
> x = x - 1 until x == 1
=> nil
> x
=> 1
> while x < 10
    x = x + 1
    puts x
  end
2
3
4
5
6
7
8
9
10
=> nil

Function

> def hello(name = 'world')
    puts "Hello #{name}"
  end
=> nil
> hello
Hello world
=> nil
> hello 'Jeoygin'
Hello Jeoygin
=> nil

Collection

Array

> arr = [8, 'blue', 1.414]
=> [8, "blue", 1.414]
> arr[0]
=> 8
> arr[-1]
=> 1.414
> arr[0..2]
=> [8, "blue", 1.414]
> arr[0...2]
=> [8, "blue"]
> (0..1).class
=> Range
> arr.push((1..3).to_a)
=> [8, "blue", 1.414, [1, 2, 3]]
> arr.pop
=> [1, 2, 3]
> arr.pop
=> 1.414
> arr[1] = nil
=> nil
> arr
=> [8, nil]
> arr = %w[blue red green yellow]
=> ["blue", "red", "green", "yellow"]
> empty1 = []
=> []
> empty2 = Array.new
=> []

Hash

> user = {
    'name' => 'Jeoygin',
     'age' => 'secret'
  }
=> {"name"=>"Jeoygin", "age"=>"secret"}
> user['name']
=> "Jeoygin"
> user['hobby']
=> nil
> dict = Hash.new(0)
=> {}
> dict['key1']
=> 0
> dict['key1'] = dict['key1'] + 1
=> 1
> dict[:array] = [1, 2, 3]
=> [1, 2, 3]
dict
=> {"key1"=>1, :array=>[1, 2, 3]}

Variable and Symbol

> 'string'.object_id
=> 70149202218820
> 'string'.object_id
=> 70149198469560
> :string.class
=> Symbol
> :string.object_id
=> 158248
> :string.object_id
=> 158248

Class and Module

> 8.class
=> Fixnum
> 8.class.superclass
=> Integer
> 8.class.superclass.superclass
=> Numeric
> 8.class.superclass.superclass.superclass
=> Object
> 8.class.superclass.superclass.superclass.superclass
=> BasicObject
8.class.superclass.superclass.superclass.superclass.superclass
=> nil
> Fixnum.class
=> Class
> Class.class
=> Class
> Class.superclass
=> Module
> Class.superclass.superclass
=> Object
> Module.class
=> Class

Class

class User
  attr_accessor :first_name, :last_name

  def initialize(first_name, last_name)
    @first_name = first_name
    @last_name = last_name
  end

  def hello()
    puts "Hello #{first_name} #{last_name}"
  end
end

> user = User.new('Jeoygin', 'Wang')
=> #<User:0x007f99c418a280 @first_name="Jeoygin", @last_name="Wang">
> user.hello
Hello Jeoygin Wang
=> nil

Ruby supports inheritance. But a class can only inherit from a single other class.

> class Admin < User
> end
=> nil
> admin = Admin.new('jeoygin', 'Wang')
=> #<Admin:0x000000013236a0 @first_name="Jeoygin", @last_name="Wang">
> admin.hello
Hello Jeoygin Wang
=> nil

Module

module Hello
  def hi
    puts "Hello " + to_s
  end
end

class Person
  include Hello
  attr_accessor :name

  def initialize(name)
    @name = name
  end

  def to_s
    name
  end
end

> Person.new('Jeoygin').hi
Hello Jeoygin
=> nil

Block

> 3.times {puts "Hello"}
Hello
Hello
Hello
=> 3
> def threeTimes
    yield
    yield
    yield
  end
=> nil
> threeTimes {puts "Hello"}
Hello
Hello
Hello
=> nil
> def call_block(&block)
    block.call
  end
=> nil
> call_block {puts "Hello block"}
Hello block
=> nil

Regular Expressions

> line = 'Perl, zero or more other chars, then Python'
=> "Perl, zero or more other chars, then Python"
> puts "Scripting language mentioned: #{line}" if line =~ /Perl|python/
Scripting language mentioned: Perl, zero or more other chars, then Python
=> nil
> line.sub(/Perl/, 'Ruby')
=> "Ruby, zero or more other chars, then Python"
> 'Python, Python, Python'.gsub(/Python/, 'Ruby')
=> "Ruby, Ruby, Ruby"

Meta Programming

Open Class

class NilClass
  def blank?
    true
  end
end

class String
  def blank?
    self.size == 0
  end
end

> ["", "tiger", nil].each do |element|
    puts element unless element.blank?
  end
tiger
=> ["", "tiger", nil]

method_missing

class Echo
  def self.method_missing name, *args
    puts ([name] << args).join(' ')
  end
end

> Echo.hello 'world'
hello world
=> nil

Source Mirror

For Chinese developers, you know that.

$ gem sources --remove https://rubygems.org/
$ gem sources -a https://ruby.taobao.org/
$ gem sources -l

Reference

• Programming Ruby: The Pragmaic Programmer’s Guide
• 七周七语言:理解多种编程范型