IRB

Introduction#

IRB means “Interactive Ruby Shell”. Basically it lets you execute ruby commands in real time (like the normal shell does).

IRB is an indispensable tool when dealing with Ruby API. Works as classical rb script. Use it for short and easy commands.

One of the nice IRB functions is that when you press tab while typing a method it will give you an advice to what you can use (This is not an IntelliSense)

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' and` inf-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
## 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'
binding.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.