Simple netstat in Ruby

netstat.rb

!#/usr/bin/env ruby

PROC_NET_TCP = '/proc/net/tcp'  # This should always be the same ...

TCP_STATES = { '00' => 'UNKNOWN',  # Bad state ... Impossible to achieve ...
               'FF' => 'UNKNOWN',  # Bad state ... Impossible to achieve ...
               '01' => 'ESTABLISHED',
               '02' => 'SYN_SENT',
               '03' => 'SYN_RECV',
               '04' => 'FIN_WAIT1',
               '05' => 'FIN_WAIT2',
               '06' => 'TIME_WAIT',
               '07' => 'CLOSE',
               '08' => 'CLOSE_WAIT',
               '09' => 'LAST_ACK',
               '0A' => 'LISTEN',
               '0B' => 'CLOSING' } # Not a valid state ...

if $0 == __FILE__

  STDOUT.sync = true
  STDERR.sync = true

  File.open(PROC_NET_TCP).each do |i|

    i = i.strip

    next unless i.match(/^\d+/)

    i = i.split(' ')

    local, remote, state = i.values_at(1, 2, 3)

    local_IP, local_port   = local.split(':').collect { |i| i.to_i(16) }
    remote_IP, remote_port = remote.split(':').collect { |i| i.to_i(16) }

    connection_state = TCP_STATES.fetch(state)

    local_IP  = [local_IP].pack('N').unpack('C4').reverse.join('.')
    remote_IP = [remote_IP].pack('N').unpack('C4').reverse.join('.')

      puts "#{local_IP}:#{local_port} " +
        "#{remote_IP}:#{remote_port} #{connection_state}"
  end

  exit(0)
end