# Basic Usage

IRB means "Interactive Ruby Shell", letting us execute ruby expressions from the standart input.

To start, type irb into your shell. You can write anything in Ruby, from simple expressions:

$ irb
2.1.4 :001 > 2+2
=> 4

to complex cases like methods:

2.1.4 :001> def method
2.1.4 :002?>   puts "Hello World"
2.1.4 :003?> end
=> :method
2.1.4 :004 > method
Hello World
=> nil

# Starting an IRB session inside a Ruby script

As of Ruby 2.4.0, you can start an interactive IRB session inside any Ruby script using these lines:

require 'irb'

This will start an IBR REPL where you will have the expected value for self and you will be able to access all local variables and instance variables that are in scope. Type Ctrl+D or quit in order to resume your Ruby program.

This can be very useful for debugging.

# Parameters

Option Details
-f Suppress read of ~/.irbrc
-m Bc mode (load mathn, fraction or matrix are available)
-d Set $DEBUG to true (same as `ruby -d')
-r load-module Same as `ruby -r'
-I path Specify $LOAD_PATH directory
-U Same as ruby -U
-E enc Same as ruby -E
-w Same as ruby -w
-W[level=2] Same as ruby -W
--inspect Use `inspect' for output (default except for bc mode)
--noinspect Don't use inspect for output
--readline Use Readline extension module
--noreadline Don't use Readline extension module
--prompt prompt-mode Switch prompt mode. Pre-defined prompt modes are default',simple', xmp' andinf-ruby'
--inf-ruby-mode Use prompt appropriate for inf-ruby-mode on emacs. Suppresses --readline.
--simple-prompt Simple prompt mode
--noprompt No prompt mode
--tracer Display trace for each execution of commands.
--back-trace-limit n Display backtrace top n and tail n. The default value is 16.
--irb_debug n Set internal debug level to n (not for popular use)
-v, --version Print the version of irb