Variables are created and set to nil as soon as they are mentioned

Tim:~> irb
>> local_variables
=> ["_"]
>> if false
>> some_variable = :yahoo
>> end
=> nil
>> some_variable
=> nil
>> local_variables
=> ["_", "some_variable"]

Isn't that interesting? When I define a variable within an if statement that will never be entered (and thus the variable will never be assigned to :yahoo), it is listed as a local variable and set to nil.

Ruby Variables

• $global variables are available from anywhere in the program--no matter the object or method, $global will be available.
• $local variables are only available with the limited context in which they are defined--within a method or block, or if defined outside of a method or block, within whatever self is (a class or module or main).
• @instance variables are available anywhere within a specific instance of an object.
• @@class variables are common to all instances of a class. They can be used to count the instance of a class, as shown in the figure above.