gistfile1.rb

require 'ping'

unless ARGV.first =~ /\d+\.\d+\.\d+\.\d+/
  puts "Bad Network address: #{ARGV.first}"
  exit 1
end

$stdout = File.open(ARGV.last,"w") if ARGV.size == 2

class_c = ARGV.first.gsub(/\d+$/,"")

255.times do |i|
  ip_address = class_c + i.to_s
  if Ping.pingecho(ip_address, 1)
    $stdout.puts "#{ip_address} is up" 
    $stdout.flush
  end
end