Counting number of TCP/IP connections established between given two processes.

ipip.rb

#!/usr/local/bin/ruby

require "pp"

if ARGV.size < 2
  $stderr.puts "Usage: ruby ipip.rb PID1 PID2"
  exit -1
end

pid_1 = ARGV[0]
pid_2 = ARGV[1]

LsofRecord = Struct.new :command, :pid, :user, :fd, :type, :device, :size, :node, :name, :state

def lsof_by_pid(pid)
  `lsof -P -p #{pid}`.lines.map {|e| LsofRecord.new(* e.split(/\s+/)) }
end

def lsof_tcp_arrow(a)
  a.select(&:name).map {|e| e.name.split(/->/) }.select {|e| e.size == 2 }
end

backet = {}
count  = 0
lsof_tcp_arrow(lsof_by_pid(pid_1)).each {|e| backet[e] = 1 }
lsof_tcp_arrow(lsof_by_pid(pid_2)).each {|e|
  count += 1 if backet[e.reverse]
}

puts count