IRB

Overview

IRB stands for “Interactive Ruby” and is a tool to interactively execute Ruby expressions read from the standard input. The irb command from your shell will start the interpreter.

IRB provides a shell-like interface that supports user interaction with the Ruby interpreter. It operates as a read-eval-print loop (REPL) that:

• Reads each character as you type. You can modify the IRB context to change the way input works. See Input.

• Evaluates the code each time it has read a syntactically complete passage.

• Prints after evaluating. You can modify the IRB context to change the way output works. See Output.

Installation

Note

IRB is a default gem of Ruby, so you shouldn’t need to install it separately. However, if you’re using Ruby 2.6 or later and want to upgrade/install a specific version of IRB, follow these steps.

To install it with bundler, add this line to your application’s Gemfile:

gem 'irb'

Then execute:

$ bundle

Or install it directly with:

$ gem install irb

Usage

Note

We’re working hard to match Pry’s variety of powerful features in IRB. Track our progress or find contribution ideas in COMPARED_WITH_PRY.md.

Starting IRB

You can start a fresh IRB session by typing irb in your terminal. In the session, you can evaluate Ruby expressions or prototype small Ruby scripts. Input is executed when it is syntactically complete.

$ irb
irb(main):001> 1 + 2
=> 3
irb(main):002* class Foo
irb(main):003*   def foo
irb(main):004*     puts 1
irb(main):005*   end
irb(main):006> end
=> :foo
irb(main):007> Foo.new.foo
1
=> nil

The binding.irb Breakpoint

If you use Ruby 2.5 or later versions, you can use binding.irb in your program as breakpoints. Once binding.irb is evaluated, a new IRB session starts with the surrounding context:

$ ruby test.rb

From: test.rb @ line 2 :

    1: def greet(word)
 => 2:   binding.irb
    3:   puts "Hello #{word}"
    4: end
    5:
    6: greet("World")

irb(main):001> word
=> "World"
irb(main):002> exit
Hello World

Debugging

You can use IRB as a debugging console with debug.gem with these options:

• In binding.irb, use the debug command to start an irb:rdbg session with access to all debug.gem commands.

• Use the RUBY_DEBUG_IRB_CONSOLE=1 environment variable to make debug.gem use IRB as the debugging console.

To learn more about debugging with IRB, see Debugging with IRB.

Startup

At startup, IRB:

1. Interprets (as Ruby code) the content of the configuration file (if given).

2. Constructs the initial session context from hash IRB.conf and from default values; the hash content may have been affected by command-line options, and by direct assignments in the configuration file.

3. Assigns the context to variable conf.

4. Assigns command-line arguments to variable ARGV.

5. Prints the prompt.

6. Puts the content of the