Maybe 
Well it works in an ruby prog.  It maybe it truly is MRI issue.

Seee if I can fire up j/iron ruby

args.rb below:
==================
require "rbconfig"


puts "The name of the progrma laucnhed is #{$0} OR #{$PROGRAM_NAME}"
ARGV.each do|a|

  puts "Argument: #{a}"
end

puts "And finally the ruby executable #{ENV['_']}"


puts File.join(Config::CONFIG["bindir"],Config::CONFIG["ruby_install_name"])
================



> From: Hassan Schroeder <hassan.schroeder / gmail.com>
> Reply-To: <ruby-talk / ruby-lang.org>
> Date: Wed, 28 Jul 2010 07:30:25 +0900
> To: ruby-talk ML <ruby-talk / ruby-lang.org>
> Subject: Re: Which Ruby is in use?
> 
> On Tue, Jul 27, 2010 at 3:10 PM, Joel VanderWerf
> <joelvanderwerf / gmail.com> wrote:
> 
>> Maybe this will work?
>> 
>>>> File.join *Config::CONFIG.values_at("bindir", "ruby_install_name")
>> => "/usr/local/bin/ruby"
> 
> Works in a Rails console, but not a Ruby program. But thanks, now
> that I consider it I should be able to work with that  :-)
> 
> -- 
> Hassan Schroeder ------------------------ hassan.schroeder / gmail.com
> twitter: @hassan
>