A programmer's best friend.

Ruby is an interpreted, high-level, general-purpose programming language which supports multiple programming paradigms. It was designed with an emphasis on programming productivity and simplicity. In Ruby, everything is an object, including primitive data types.

History of Ruby

The first public release of Ruby 0.95 was announced on Japanese domestic newsgroups on December 21, 1995. Subsequently, three more versions of Ruby were released in two days. The release coincided with the launch of the Japanese-language ruby-list mailing list, which was the first mailing list for the new language.

Already present at this stage of development were many of the features familiar in later releases of Ruby, including object-oriented design, classes with inheritance, mixins, iterators, closures, exception handling and garbage collection.

After the release of Ruby 0.95 in 1995, several stable versions of Ruby were released in these years:

• Ruby 1.0: December 25, 1996
  
• Ruby 1.2: December 1998
  
• Ruby 1.4: August 1999
  
• Ruby 1.6: September 2000

In 1997, the first article about Ruby was published on the Web. In the same year, Matsumoto was hired by netlab.jp to work on Ruby as a full-time developer.

In 1998, the Ruby Application Archive was launched by Matsumoto, along with a simple English-language homepage for Ruby.

In 1999, the first English language mailing list ruby-talk began, which signaled a growing interest in the language outside Japan. In this same year, Matsumoto and Keiju Ishitsuka wrote the first book on Ruby, The Object-oriented Scripting Language Ruby (オブジェクト指向スクリプト言語 Ruby), which was published in Japan in October 1999. It would be followed in the early 2000s by around 20 books on Ruby published in Japanese.

By 2000, Ruby was more popular than Python in Japan. In September 2000, the first English language book Programming Ruby was printed, which was later freely released to the public, further widening the adoption of Ruby amongst English speakers. In early 2002, the English-language ruby-talk mailing list was receiving more messages than the Japanese-language ruby-list, demonstrating Ruby's increasing popularity in the non-Japanese speaking world.

Ruby 1.8 and 1.9

Ruby 1.8 was initially released August 2003, was stable for a long time, and was retired June 2013. Although deprecated, there is still code based on it. Ruby 1.8 is only partially compatible with Ruby 1.9.

Ruby 1.8 has been the subject of several industry standards. The language specifications for Ruby were developed by the Open Standards Promotion Center of the Information-Technology Promotion Agency (a Japanese government agency) for submission to the Japanese Industrial Standards Committee (JISC) and then to the International Organization for Standardization (ISO). It was accepted as a Japanese Industrial Standard (JIS X 3017) in 2011 and an international standard (ISO/IEC 30170) in 2012.

Around 2005, interest in the Ruby language surged in tandem with Ruby on Rails, a web framework written in Ruby. Rails is frequently credited with increasing awareness of Ruby.

Effective with Ruby 1.9.3, released October 31, 2011, Ruby switched from being dual-licensed under the Ruby License and the GPL to being dual-licensed under the Ruby License and the two-clause BSD license. Adoption of 1.9 was slowed by changes from 1.8 that required many popular third party gems to be rewritten. Ruby 1.9 introduces many significant changes over the 1.8 series. Examples include:

• block local variables (variables that are local to the block in which they are declared)
• an additional lambda syntax: f = ->(a,b) { puts a + b }
• an additional Hash literal syntax using colons for symbol keys: {symbol_key: "value"} == {:symbol_key => "value"}
• per-string character encodings are supported
• new socket API (IPv6 support)
• require_relative import security

Ruby 2

Ruby 2.0 was intended to be fully backward compatible with Ruby 1.9.3. As of the official 2.0.0 release on February 24, 2013, there were only five known (minor) incompatibilities. Ruby 2.0 added several new features, including:

• method keyword arguments,
• a new method, Module#prepend, for extending a class,
• a new literal for creating an array of symbols,
• new API for the lazy evaluation of Enumerables, and
• a new convention of using #to_h to convert objects to Hashes. Starting with 2.1.0, Ruby's versioning policy changed to be more similar to semantic versioning.

Ruby 2.2.0 includes speed-ups, bugfixes, and library updates and removes some deprecated APIs. Most notably, Ruby 2.2.0 introduces changes to memory handling – an incremental garbage collector, support for garbage collection of symbols and the option to compile directly against jemalloc. It also contains experimental support for using vfork(2) with system() and spawn(), and added support for the Unicode 7.0 specification. Since version 2.2.1, Ruby MRI performance on PowerPC64 was improved. Features that were made obsolete or removed include callcc, the DL library, Digest::HMAC, lib/rational.rb, lib/complex.rb, GServer, Logger::Application as well as various C API functions.

Ruby 3

Ruby 3.0.0 was released on Christmas Day in 2020. It is known as Ruby 3x3 which means that programs would run three times faster in Ruby 3.0 comparing to Ruby 2.0. and some had already implemented in intermediate releases on the road from 2 to 3. To achieve 3x3, Ruby 3 comes with MJIT, and later YJIT, Just-In-Time Compilers, to make programs faster, although they are described as experimental and remain disabled by default (enabled by flags at runtime).

Another goal of Ruby 3.0 is to improve concurrency and two more utilities Fibre Scheduler, and experimental Ractor facilitate the goal. Ractor is light-weight and thread-safe as it is achieved by exchanging messages rather than shared objects.

Ruby 3.0 introduces RBS language to describe the types of Ruby programs for static analysis. It is separated from general Ruby programs.

There are some syntax enhancements and library changes in Ruby 3.0 as well.

Ruby 3.1 was released on Christmas Day in 2021. It includes YJIT, a new, experimental, Just-In-Time Compiler developed by Shopify, to enhance the performance of real world business applications. A new debugger is also included. There are some syntax enhancements and other improvements in this release. Network libraries for FTP, SMTP, IMAP, and POP are moved from default gems to bundled gems.

Semantics and philosophy

Ruby is object-oriented: every value is an object, including classes and instances of types that many other languages designate as primitives (such as integers, booleans, and "null"). Variables always hold references to objects. Every function is a method and methods are always called on an object. Methods defined at the top level scope become methods of the Object class. Since this class is an ancestor of every other class, such methods can be called on any object. They are also visible in all scopes, effectively serving as "global" procedures. Ruby supports inheritance with dynamic dispatch, mixins and singleton methods (belonging to, and defined for, a single instance rather than being defined on the class). Though Ruby does not support multiple inheritance, classes can import modules as mixins.

Ruby has been described as a multi-paradigm programming language: it allows procedural programming (defining functions/variables outside classes makes them part of the root, 'self' Object), with object orientation (everything is an object) or functional programming (it has anonymous functions, closures, and continuations; statements all have values, and functions return the last evaluation). It has support for introspection, reflection and metaprogramming, as well as support for interpreter-based threads. Ruby features dynamic typing, and supports parametric polymorphism.

According to the Ruby FAQ, the syntax is similar to Perl's and the semantics are similar to Smalltalk's, but the design philosophy differs greatly from Python's. Ruby 3.2 was released on Christmas Day in 2022. It brings support for being run inside of a WebAssembly environment via a WASI interface. Regular expressions also receives some improvements, including a faster, memoized matching algorithm to protect against certain ReDoS attacks, and configurable timeouts for regular expression matching. Additional debugging and syntax features are also included in this release, which include syntax suggestion, as well as error highlighting. The MJIT compiler has been re-implemented as a standard library module, while the YJIT, a Rust-based JIT compiler now supports more architectures on Linux.

Features

• Thoroughly object-oriented with inheritance, mixins and metaclasses
• Dynamic typing and duck typing
• Everything is an expression (even statements) and everything is executed imperatively (even declarations)
• Succinct and flexible syntax that minimizes syntactic noise and serves as a foundation for domain-specific languages
• Dynamic reflection and alteration of objects to facilitate metaprogramming
• Lexical closures, iterators and generators, with a block syntax
• Literal notation for arrays, hashes, regular expressions and symbols
• Embedding code in strings (interpolation)
• Default arguments
• Four levels of variable scope (global, class, instance, and local) denoted by sigils or the lack thereof
• Garbage collection
• First-class continuations
• Strict boolean coercion rules (everything is true except false and nil)
• Exception handling
• Operator overloading
• Built-in support for rational numbers, complex numbers and arbitrary-precision arithmetic
• Custom dispatch behavior (through method_missing and const_missing)
• Native threads and cooperative fibers (fibers are a 1.9/YARV feature)
• Support for Unicode and multiple character encodings.
• Native plug-in API in C
• Interactive Ruby Shell, an interactive command-line interpreter that can be used to test code quickly (REPL)
• Centralized package management through RubyGems
• Implemented on all major platforms
• Large standard library, including modules for YAML, JSON, XML, CGI, OpenSSL, HTTP, FTP, RSS, curses, zlib and Tk
• Just-in-time compilation

Syntax

The syntax of the Ruby programming language is broadly similar to that of Perl and Python. Class and method definitions are signaled by keywords, whereas code blocks can be defined by either keywords or braces. In contrast to Perl, variables are not obligatorily prefixed with a sigil. When used, the sigil changes the semantics of scope of the variable. For practical purposes there is no distinction between expressions and statements. Line breaks are significant and taken as the end of a statement; a semicolon may be equivalently used. Unlike Python, indentation is not significant.

One of the differences from Python and Perl is that Ruby keeps all of its instance variables completely private to the class and only exposes them through accessor methods (attr_writer, attr_reader, etc.). Unlike the "getter" and "setter" methods of other languages like C++ or Java, accessor methods in Ruby can be created with a single line of code via metaprogramming; however, accessor methods can also be created in the traditional fashion of C++ and Java. As invocation of these methods does not require the use of parentheses, it is trivial to change an instance variable into a full function without modifying a single line of calling code or having to do any refactoring achieving similar functionality to C# and VB.NET property members.

Interactive sessions

The following examples can be run in a Ruby shell such as Interactive Ruby Shell, or saved in a file and run from the command line by typing ruby <filename>.

Classic Hello world example:

puts 'Hello World!'

Some basic Ruby code:

# Everything, including a literal, is an object, so this works:
-199.abs # => 199
'ice is nice'.length # => 11
'ruby is cool.'.index('u') # => 1
"Nice Day Isn't It?".downcase.split('').uniq.sort.join
# => " '?acdeinsty"

Input:

print 'Please type name >'
name = gets.chomp
puts "Hello #{name}."

Conversions:

puts 'Give me a number'
number = gets.chomp
puts number.to_i
output_number = number.to_i + 1
puts output_number.to_s + ' is a bigger number.'

Strings

There are a variety of ways to define strings in Ruby.

The following assignments are equivalent:

a = "\nThis is a double-quoted string\n"
a = %Q{\nThis is a double-quoted string\n}
a = %{\nThis is a double-quoted string\n}
a = %/\nThis is a double-quoted string\n/
a = <<-BLOCK

This is a double-quoted string
BLOCK

Strings support variable interpolation:

var = 3.14159
"pi is #{var}"
=> "pi is 3.14159"

The following assignments are equivalent and produce raw strings:

a = 'This is a single-quoted string'
a = %q{This is a single-quoted string}

Collections

Constructing and using an array:

a = [3, 'hello', 14.5, 1, 2, [6, 15]]

a[2] # => 14.5
a.[](2) # => 14.5
a.reverse # => [[6, 15], 2, 1, 14.5, 'hello', 3]
a.flatten.uniq # => [3, 'hello', 14.5, 1, 2, 6, 15]

Constructing and using an associative array (in Ruby, called a hash):

hash = Hash.new # equivalent to hash = {}
hash = { water: 'wet', fire: 'hot' } # makes the previous line redundant as we are now
 # assigning hash to a new, separate hash object
puts hash[:fire] # prints "hot"

hash.each_pair do |key, value| # or: hash.each do |key, value|
 puts "#{key} is #{value}"
end
# returns {:water=>"wet", :fire=>"hot"} and prints:
# water is wet
# fire is hot

hash.delete :water # deletes the pair :water => 'wet' and returns "wet"
hash.delete_if {|key,value| value == 'hot'} # deletes the pair :fire => 'hot' and returns {}

Control structures

If statement:

# Generate a random number and print whether it's even or odd.
if rand(100).even?
 puts "It's even"
else
 puts "It's odd"
end

Blocks and iterators

The two syntaxes for creating a code block:

{ puts 'Hello, World!' } # note the braces
# or:
do
 puts 'Hello, World!'
end

A code block can be passed to a method as an optional block argument. Many built-in methods have such arguments:

File.open('file.txt', 'w') do |file| # 'w' denotes "write mode"
 file.puts 'Wrote some text.'
end # file is automatically closed here

File.readlines('file.txt').each do |line|
 puts line
end
# => Wrote some text.

Parameter-passing a block to be a closure:

# In an object instance variable (denoted with '@'), remember a block.
def remember(&a_block)
 @block = a_block
end

# Invoke the preceding method, giving it a block that takes a name.
remember {|name| puts "Hello, #{name}!"}

# Call the closure (note that this happens not to close over any free variables):
@block.call('Jon') # => "Hello, Jon!"

Creating an anonymous function:

proc {|arg| puts arg}
Proc.new {|arg| puts arg}
lambda {|arg| puts arg}
->(arg) {puts arg} # introduced in Ruby 1.9

Returning closures from a method:

def create_set_and_get(initial_value=0) # note the default value of 0
 closure_value = initial_value
 [ Proc.new {|x| closure_value = x}, Proc.new { closure_value } ]
end

setter, getter = create_set_and_get # returns two values
setter.call(21)
getter.call # => 21

# Parameter variables can also be used as a binding for the closure,
# so the preceding can be rewritten as:

def create_set_and_get(closure_value=0)
 [ proc {|x| closure_value = x } , proc { closure_value } ]
end

Yielding the flow of program control to a block that was provided at calling time:

def use_hello
 yield "hello"
end

# Invoke the preceding method, passing it a block.
use_hello {|string| puts string} # => 'hello'

Iterating over enumerations and arrays using blocks:

array = [1, 'hi', 3.14]
array.each {|item| puts item }
# prints:
# 1
# 'hi'
# 3.14

array.each_index {|index| puts "#{index}: #{array[index]}" }
# prints:
# 0: 1
# 1: 'hi'
# 2: 3.14

# The following uses a (a..b) Range
(3..6).each {|num| puts num }
# prints:
# 3
# 4
# 5
# 6

# The following uses a (a...b) Range
(3...6).each {|num| puts num }
# prints:
# 3
# 4
# 5

A method such as inject can accept both a parameter and a block. The inject method iterates over each member of a list, performing some function on it while retaining an aggregate. This is analogous to the foldl function in functional programming languages. For example:

[1,3,5].inject(10) {|sum, element| sum + element} # => 19

On the first pass, the block receives 10 (the argument to inject) as sum, and 1 (the first element of the array) as element. This returns 11, which then becomes sum on the next pass. It is added to 3 to get 14, which is then added to 5 on the third pass, to finally return 19.

Using an enumeration and a block to square the numbers 1 to 10 (using a range):

(1..10).collect {|x| x*x} # => [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

Or invoke a method on each item (map is a synonym for collect):

(1..5).map(&:to_f) # => [1.0, 2.0, 3.0, 4.0, 5.0]

Classes

The following code defines a class named Person. In addition to initialize, the usual constructor to create new objects, it has two methods: one to override the <=> comparison operator (so Array#sort can sort by age) and the other to override the to_s method (so Kernel#puts can format its output). Here, attr_reader is an example of metaprogramming in Ruby: attr_accessor defines getter and setter methods of instance variables, but attr_reader only getter methods. The last evaluated statement in a method is its return value, allowing the omission of an explicit return statement.

class Person
 attr_reader :name, :age
 def initialize(name, age)
 @name, @age = name, age
 end
 def <=>(person) # the comparison operator for sorting
 @age <=> person.age
 end
 def to_s
 "#{@name} (#{@age})"
 end
end

group = [
 Person.new("Bob", 33),
 Person.new("Chris", 16),
 Person.new("Ash", 23)
]

puts group.sort.reverse

The preceding code prints three names in reverse age order:

Bob (33)
Ash (23)
Chris (16)

Person is a constant and is a reference to a Class object.

Open classes

In Ruby, classes are never closed: methods can always be added to an existing class. This applies to all classes, including the standard, built-in classes. All that is needed to do is open up a class definition for an existing class, and the new contents specified will be added to the existing contents. A simple example of adding a new method to the standard library's Time class:

# re-open Ruby's Time class
class Time
 def yesterday
   self - 86400
 end
end

today = Time.now # => 2013-09-03 16:09:37 +0300
yesterday = today.yesterday # => 2013-09-02 16:09:37 +0300

Adding methods to previously defined classes is often called monkey-patching. If performed recklessly, the practice can lead to both behavior collisions with subsequent unexpected results and code scalability problems.

Since Ruby 2.0 it has been possible to use refinements to reduce the potentially negative consequences of monkey-patching, by limiting the scope of the patch to particular areas of the code base.

# re-open Ruby's Time class
module RelativeTimeExtensions
 refine Time do
   def half_a_day_ago
     self - 43200
   end
 end
end

module MyModule
 class MyClass
   # Allow the refinement to be used
   using RelativeTimeExtensions

   def window
     Time.now.half_a_day_ago
   end
 end
end

Exceptions

An exception is raised with a raise call:

raise

An optional message can be added to the exception:

raise "This is a message"

Exceptions can also be specified by the programmer:

raise ArgumentError, "Illegal arguments!"

Alternatively, an exception instance can be passed to the raise method:

raise ArgumentError.new("Illegal arguments!")

This last construct is useful when raising an instance of a custom exception class featuring a constructor that takes more than one argument:

class ParseError < Exception
 def initialize(input, line, pos)
 super "Could not parse '#{input}' at line #{line}, position #{pos}"
 end
end

raise ParseError.new("Foo", 3, 9)

Exceptions are handled by the rescue clause. Such a clause can catch exceptions that inherit from StandardError. Other flow control keywords that can be used when handling exceptions are else and ensure:

begin
 # do something
rescue
 # handle exception
else
 # do this if no exception was raised
ensure
 # do this whether or not an exception was raised
end

It is a common mistake to attempt to catch all exceptions with a simple rescue clause. To catch all exceptions one must write:

begin
 # do something
rescue Exception
 # Exception handling code here.
 # Don't write only "rescue"; that only catches StandardError, a subclass of Exception.
end

Or catch particular exceptions:

begin
 # do something
rescue RuntimeError
 # handle only RuntimeError and its subclasses
end

It is also possible to specify that the exception object be made available to the handler clause:

begin
 # do something
rescue RuntimeError => e
 # handling, possibly involving e, such as "puts e.to_s"
end

Alternatively, the most recent exception is stored in the magic global $!.

Several exceptions can also be caught:

begin
 # do something
rescue RuntimeError, Timeout::Error => e
 # handling, possibly involving e
end

Metaprogramming

Ruby code can programmatically modify, at runtime, aspects of its own structure that would be fixed in more rigid languages, such as class and method definitions. This sort of metaprogramming can be used to write more concise code and effectively extend the language.

For example, the following Ruby code generates new methods for the built-in String class, based on a list of colors. The methods wrap the contents of the string with an HTML tag styled with the respective color.

COLORS = { black: "000",
 red: "f00",
 green: "0f0",
 yellow: "ff0",
 blue: "00f",
 magenta: "f0f",
 cyan: "0ff",
 white: "fff" }

class String
 COLORS.each do |color,code|
 define_method "in_#{color}" do
 "<span style=\"color: ##{code}\">#{self}</span>"
 end
 end
end

The generated methods could then be used like this:

"Hello, World!".in_blue
 => "<span style=\"color: #00f\">Hello, World!</span>"

To implement the equivalent in many other languages, the programmer would have to write each method (in_black, in_red, in_green, etc.) separately.

Some other possible uses for Ruby metaprogramming include:

• intercepting and modifying method calls
• implementing new inheritance models
• dynamically generating classes from parameters
• automatic object serialization
• interactive help and debugging

Implementations

Matz's Ruby interpreter

The original Ruby interpreter is often referred to as Matz's Ruby Interpreter or MRI. This implementation is written in C and uses its own Ruby-specific virtual machine.

The standardized and retired Ruby 1.8 implementation was written in C, as a single-pass interpreted language.

Starting with Ruby 1.9, and continuing with Ruby 2.x and above, the official Ruby interpreter has been YARV ("Yet Another Ruby VM"), and this implementation has superseded the slower virtual machine used in previous releases of MRI.

Alternative implementations

As of 2018, there are a number of alternative implementations of Ruby, including JRuby, Rubinius, and mruby. Each takes a different approach, with JRuby and Rubinius providing just-in-time compilation and mruby also providing ahead-of-time compilation.

Ruby has three major alternative implementations:

JRuby, a mixed Java and Ruby implementation that runs on the Java virtual machine. JRuby currently targets Ruby 3.1.x. TruffleRuby, a Java implementation using the Truffle language implementation framework with GraalVM Rubinius, a C++ bytecode virtual machine that uses LLVM to compile to machine code at runtime. The bytecode compiler and most core classes are written in pure Ruby. Rubinius currently targets Ruby 2.3.1. Other Ruby implementations include:

MagLev, a Smalltalk implementation that runs on GemTalk Systems' GemStone/S VM mruby, an implementation designed to be embedded into C code, in a similar vein to Lua. It is currently being developed by Yukihiro Matsumoto and others RGSS, or Ruby Game Scripting System, a proprietary implementation that is used by the RPG Maker series of software for game design and modification of the RPG Maker engine julializer, a transpiler (partial) from Ruby to Julia. It can be used for a large speedup over e.g. Ruby or JRuby implementations (may only be useful for numerical code). Topaz, a Ruby implementation written in Python Opal, a web-based interpreter that compiles Ruby to JavaScript Other now defunct Ruby implementations were:

MacRuby, a Mac OS X implementation on the Objective-C runtime. Its iOS counterpart is called RubyMotion IronRuby an implementation on the .NET Framework Cardinal, an implementation for the Parrot virtual machine Ruby Enterprise Edition, often shortened to ree, an implementation optimized to handle large-scale Ruby on Rails projects HotRuby, a JavaScript and ActionScript implementation of the Ruby programming language The maturity of Ruby implementations tends to be measured by their ability to run the Ruby on Rails (Rails) framework, because it is complex to implement and uses many Ruby-specific features. The point when a particular implementation achieves this goal is called "the Rails singularity". The reference implementation, JRuby, and Rubinius are all able to run Rails unmodified in a production environment.

Platform support

Matsumoto originally developed Ruby on the 4.3BSD-based Sony NEWS-OS 3.x, but later migrated his work to SunOS 4.x, and finally to Linux. By 1999, Ruby was known to work across many different operating systems. Modern Ruby versions and implementations are available on all major desktop, mobile and server-based operating systems. Ruby is also supported across a number of cloud hosting platforms like Jelastic, Heroku, Google Cloud Platform and others.

Tools such as RVM and RBEnv, facilitate installation and partitioning of multiple ruby versions, and multiple 'gemsets' on one machine.