ip.rb

#!/usr/bin/env ruby

require 'socket'

class IP
  def self.local
    orig, Socket.do_not_reverse_lookup = Socket.do_not_reverse_lookup, true

    UDPSocket.open { |s| s.connect('64.233.187.99', 1); s.addr.last }
  ensure
    Socket.do_not_reverse_lookup = orig
  end

  def self.external
    `curl -s http://checkip.dyndns.org | sed 's/[a-zA-Z/<> :]//g'`
  end
end

puts IP.local, IP.external if $0 == __FILE__