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.

Answer 2

defined? is a function that returns nil if the item is undefined.

defined? somevar
=> nil
somevar = 12
defined? somevar
=> "local-variable"

So:

if defined?(somevar)
  do_something
end

Answer 3

Keep in mind that defined? returns a string if the variable is defined, nil if it isn't, so use conditional checking on its results. I think the syntax alludes that it would return a boolean.

Answer 4

All use cases :

defined? ur_variable
=> nil

ur_variable= 12
defined? ur_variable
=> "local-variable"

another_variable = nil
defined? another_variable
=> "local-variable"

Answer 5

Can also test this way.

   if somevar.nil
        # not set do something
    else
        # is set do something else
    end