debugee.rb

#!/usr/bin/env ruby
require 'rubygems'
require 'ruby-debug'
Debugger.start

def pow(x, n)
  debugger if n == 1 # start debugger when n == 1
  raise if n < 0
  if n == 0
    return 1
  else
    return pow(x, n - 1) * x
  end
end

puts pow(ARGV[0].to_i, ARGV[1].to_i)