what_connects.rb

# run like this:
#   sudo ruby -rubygems what_connects.rb 3000
#

require 'socket'
serv = TCPServer.new(ARGV[0].to_i)
begin
  sock = serv.accept_nonblock
rescue Errno::EAGAIN, Errno::ECONNABORTED, Errno::EPROTO, Errno::EINTR
  IO.select([serv])
  retry
end

puts "Connected to port 3000:"
puts %x[lsof -n -i :#{ARGV[0]}].strip

sock.close