IRB

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.

• Installation
• Usage
  • The irb Executable
  • The binding.irb Breakpoint
• Commands
• Debugging with IRB
  • More about debug.gem
  • Advantages Over debug.gem's Console
• Configuration
  • Environment Variables
• Documentation
• Extending IRB
• Development
• Contributing
• Releasing
• License

Installation

Note

IRB is a default gem of Ruby so you shouldn't need to install it separately.

But if you're using Ruby 2.6 or later and want to upgrade/install a specific version of IRB, please follow these steps.

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

gem 'irb'

And then execute:

$ bundle

Or install it directly with:

$ gem install irb

Usage

The irb Executable

You can start a fresh IRB session by typing irb in your terminal.

In the session, you can evaluate Ruby expressions or even prototype a small Ruby script. An 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 also use binding.irb in your program as breakpoints.

Once a binding.irb is evaluated, a new IRB session will be started 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):001:0> word
=> "World"
irb(main):002:0> exit
Hello World

Commands

The following commands are available on IRB. You can get the same output from the show_cmds command.

Workspace
  cwws           Show the current workspace.
  chws           Change the current workspace to an object.
  workspaces     Show workspaces.
  pushws         Push an object to the workspace stack.
  popws          Pop a workspace from the workspace stack.

IRB
  irb_load       Load a Ruby file.
  irb_require    Require a Ruby file.
  source         Loads a given file in the current session.
  irb_info       Show information about IRB.
  show_cmds      List all available commands and their description.

Multi-irb (DEPRECATED)
  irb            Start a child IRB.
  jobs           List of current sessions.
  fg             Switches to the session of the given number.
  kill           Kills the session with the given number.

Debugging
  debug          Start the debugger of debug.gem.
  break          Start the debugger of debug.gem and run its `break` command.
  catch          Start the debugger of debug.gem and run its `catch` command.
  next           Start the debugger of debug.gem and run its `next` command.
  delete         Start the debugger of debug.gem and run its `delete` command.
  step           Start the debugger of debug.gem and run its `step` command.
  continue       Start the debugger of debug.gem and run its `continue` command.
  finish         Start the debugger of debug.gem and run its `finish` command.
  backtrace      Start the debugger of debug.gem and run its `backtrace` command.
  info           Start the debugger of debug.gem and run its `info` command.

Misc
  edit           Open a file with the editor command defined with `ENV["VISUAL"]` or `ENV["EDITOR"]`.
  measure        `measure` enables the mode to measure processing time. `measure :off` disables it.

Context
  help           [DEPRECATED] Enter the mode to look up RI documents.
  show_doc       Enter the mode to look up RI documents.
  ls             Show methods, constants, and variables. `-g [query]` or `-G [query]` allows you to filter out the output.
  show_source    Show the source code of a given method or constant.
  whereami       Show the source code around binding.irb again.

Debugging with IRB

Starting from version 1.8.0, IRB boasts a powerful integration with debug.gem, providing a debugging experience akin to pry-byebug.

After hitting a binding.irb breakpoint, you can activate the debugger with the debug command. Alternatively, if the debug method happens to already be defined in the current scope, you can call irb_debug.

From: test.rb @ line 3 :

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

irb(main):001> debug
irb:rdbg(main):002>

Once activated, the prompt's header changes from irb to irb:rdbg, enabling you to use any of debug.gem's commands:

irb:rdbg(main):002> info # use info command to see available variables
%self = main
_ = nil
word = "World"
irb:rdbg(main):003> next # use next command to move to the next line
[1, 7] in test.rb
     1|
     2| def greet(word)
     3|   binding.irb
=>   4|   puts "Hello #{word}"
     5| end
     6|
     7| greet("World")
=>#0    Object#greet(word="World") at test.rb:4
  #1    <main> at test.rb:7
irb:rdbg(main):004>

Simultaneously, you maintain access to IRB's commands, such as show_source:

irb:rdbg(main):004> show_source greet

From: test.rb:2

def greet(word)
  binding.irb
  puts "Hello #{word}"
end

More about debug.gem

debug.gem offers many advanced debugging features that simple REPLs can't provide, including:

• Step-debugging
• Frame navigation
• Setting breakpoints with commands
• Thread control
• ...and many more

To learn about these features, please refer to debug.gem's commands list.

In the irb:rdbg session, the show_cmds command will also display all commands from debug.gem.

Advantages Over debug.gem's Console

This integration offers several benefits over debug.gem's native console:

1. Access to handy IRB commands like show_source or show_doc.
2. Support for multi-line input.
3. Symbol shortcuts such as @ (whereami) and $ (show_source).
4. Autocompletion.
5. Customizable prompt.

However, there are also some limitations to be aware of:

1. binding.irb doesn't support pre and do arguments like binding.break.
2. As IRB doesn't currently support remote-connection, it can't be used with debug.gem's remote debugging feature.
3. Access to the previous return value via the underscore _ is not supported.

Configuration

Environment Variables

• NO_COLOR: Assigning a value to it disables IRB's colorization.
• IRB_USE_AUTOCOMPLETE: Setting it to false disables IRB's autocompletion.
• VISUAL: Its value would be used to open files by the edit command.
• EDITOR: Its value would be used to open files by the edit command if VISUAL is unset.
• IRBRC: The file specified would be evaluated as IRB's rc-file.

Documentation

https://docs.ruby-lang.org/en/master/IRB.html

Extending IRB

IRB is currently going through some refactoring to bring in some cool improvements and make things more flexible for developers. We know that in the past, due to a lack of public APIs and documentation, many of you have had to use IRB's private APIs and components to extend it. We also know that changes can be a bit annoying and might mess with your current setup.

We're sorry if this causes a bit of a scramble. We're working hard to make IRB better and your input is super important to us. If you've been using private APIs or components in your projects, we'd love to hear about your use cases. Please feel free to file a new issue. Your feedback will be a massive help in guiding us on how to design and prioritize the development of official APIs in the future.

Right now, we've got command extension APIs on the drawing board, as you can see in #513. We've also got a prototype for helper method extension APIs in the works, as shown in #588.

We really appreciate your understanding and patience during this transition. We're pretty excited about the improvements these changes will bring to the IRB ecosystem and we hope you are too!

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ruby/irb.

Releasing

rake release
gh release create vX.Y.Z --generate-notes

License

The gem is available as open source under the terms of the 2-Clause BSD License.