execute_only_if.rb

#!/usr/bin/env ruby

class HelloWorld
   def initialize 
      @msg = "HelloWorld!"
   end

   def to_s
      return @msg
   end
end

#Only execute if called directly
#ie other file can require/include and this part will not be executed
# $0 calling file (eneterd at command line)
# __FILE__ This file

if $0 == __FILE__
   hi_world = HelloWorld.new
   puts hi_world
end

Cheers Morgan!