gistfile1.txt

require 'ipaddr'

ips = IPAddr.new("192.168.1.0/24").to_range.to_a[1..-2]

pings = ips.map do |ipaddr|
  ip = ipaddr.to_s
  pid = spawn("ping -q -W 2 -c 1 #{ip}", [:err, :out] => "/dev/null")
  [pid, ip]
end

def arp_spawn(ip)
  rout, wout = IO.pipe
  pid = spawn("arp #{ip} | awk '{ print $4 }'", out: wout, err: "/dev/null")
  wout.close
  [pid, ip, rout]
end

arps = []
pings.each do |pid, ip|
  Process.wait(pid)
  arps << arp_spawn(ip) if $?.exitstatus.zero? # online
end

arps.each do |pid, ip, rout|
  Process.wait(pid)
  p "#{ip} #{rout.read.strip}" # ip, mac
  rout.close
end