$: in Ruby

In Rails programming you might seldom come across the below statement

Copy$:.unshift File.dirname(__FILE__)

$: represents load path in Ruby.
Its a pre-defined variable and short hand for $LOAD_PATH which ruby uses to look for files.

unshift prepends the given path to the beginning of the array (load path).

__FILE__ gives the relative path of the file from the current execution directory.
Incase, you need absolute path, use

CopyFile.expand_path(__FILE__)

NOTE : This explanation is as of Ruby 1.8.6. Latest versions of Ruby behave differently.