get ruby process pid using pty lib

main.rb

#!/usr/bin/env ruby
# conding: utf-8

#
# this script shows pid which contains 'ruby'
#
require 'pty'

cmd = 'ps aux | grep ruby'
PTY.spawn(cmd) do |reader, writer, pid|
  val = reader.readlines.collect {|line| line.chomp }
  puts val.first.split(' ')[1]
end