server_select.rb

require "socket"  
@echo_server = TCPServer.new('localhost', 2200)  
@socket_list = Array.new
@socket_list.push @echo_server
loop do  
  return_array = select( @socket_list, nil, nil, nil )
  res = return_array[0][0]
  if res == @echo_server
    client=res.accept
    @socket_list.push client
    puts "#{client.peeraddr[2]}:#{client.peeraddr[1]} is connected"
  else
    data = res.recvfrom( 20 )[0].chomp
    if data =="exit"
      res.puts "bye!"
      puts "#{res.peeraddr[2]}:#{res.peeraddr[1]} is disconnect"
      res.close
      @socket_list.delete res
    else
      puts "I only received 20 bytes '#{data}' from #{res.peeraddr[2]}:#{res.peeraddr[1]}"
      res.puts "You said: #{data}"
    end
  end
end