The following line acts differently under rdebug and ruby
  if __FILE__ == $0

FXRuby has the line, above, in nearly all its sample code.
  

Under rdebug, the value of $0 is, on my system,
  F:/InstantRails-2.0-win/ruby/bin/rdebug

Executing
  ruby -rdebug UltraDedup.rb
then the value of $0 is
  Debug.rb


Executing
  ruby UltraDedup.rb
then the value of $0 is
  UltraDededup.rb


How can I change things so that
  if __FILE__ == $0
acts correctly in each environment?

Ralph