Testing for undefined variables in Ruby a la JavaScript?

Question

In JavaScript there's a useful way to test for a variable which has never been defined at any given point. For example, the following snippet of code will return true if the variable bob has not been defined:

typeof(bob)=='undefined' 

How do I accomplish the same test in Ruby?

edit: I'm looking for a test which is equally compact in nature. I've come up with some awkward approximations using exceptions and such, but those aren't very pretty!

Answer 1

defined?(variable_name)  irb(main):004:0> defined?(foo) => nil irb(main):005:0> foo = 1 => 1 irb(main):006:0> defined?(foo) => "local-variable" 

Here is a good write up on it.