Interactive Ruby (irb)

If you type "irb" in the terminal, you'll get the following screen ...

You can type a ruby code on the terminal, for example, it'll return 14 if you type 7+7.

You can also create a function. For example, function hi will print "Hello World!!!" on the screen.

Moreover, you can enter any ruby commands on the terminal.
Finally, irb'll help you to test any ruby commands without wasting your time because irb runs the ruby command immediately.