.RB File Format

Introduction

A .rb file holds source code in Ruby, the dynamic, object-oriented language created by Yukihiro Matsumoto and first released to the public in 1995. A Ruby program is plain text, read and run by the ruby command with no separate compile step.

The same language is used in several other kinds of file, told apart by extension or by name:

All of these are ordinary Ruby: each is run by a Ruby interpreter, in a context that makes some extra methods available.

Structure

A Ruby file is text, in UTF-8 unless a comment on its first line says otherwise. There is no required shape and no entry point: expressions run from the top of the file to the bottom, and class and method definitions are themselves expressions that run as they are reached. A line consisting of __END__ ends the program, and anything after it is data the program can read.

#!/usr/bin/env ruby
# frozen_string_literal: true

require "json"

class Greeter
  def initialize(name)
    @name = name
  end

  def greet = "Hello, #{@name}"
end

puts Greeter.new("world").greet

What this page does not cover

This overview is the only page of the reference so far. It describes the kinds of file that hold Ruby and their overall layout. It does not yet describe the language itself: lexical structure, literals, types, variables, expressions, control flow, methods, blocks, classes and modules, refinements, exceptions, pattern matching, regular expressions, loading and gems, concurrency, the standard library, the versions of Ruby, or the contents of Rakefile, Gemfile, .gemspec and .ru files. Until those pages exist, the Ruby syntax documentation is the place to read about them.

Links