The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

21.3. Using irb

The irb utility (interactive Ruby) has been distributed with Ruby for many years. It can be thought of as a “testbed” or “playground” where you try out quick hacks and new ideas.

Basic usage of irb is simple. When you start it, you get a prompt where you can type Ruby expressions; each expression is evaluated, and the result is printed for you. Here’s a small example of a session:

$ irb
irb(main):001:0> "cell" + "o"
=> "cello"
irb(main):002:0> 3*79
=> 237
irb(main):003:0> Dir.entries(".").size
=> 17
irb(main):004:0> rand
=> 0.850757389880155
irb(main):005:0> rand
=> 0.679879756672551
irb(main):006:0> defined? foo
=> nil
irb(main):007:0> defined? Object
=> "constant"
irb(main):008:0> quit
$

Of course, it’s more than just a calculator. ...