How to ping a list of IP adresses to check if they are still in use

test.rb

ips = File.readlines("ip_list").map(&:strip)
used_ips = []
if File.exist?("used_ips")
  used_ips = File.readlines("used_ips").map(&:strip)
end


ips -= used_ips

while ips.size > 0 do
  puts "Starting new round..."
  ips.each do |ip|
    puts "Trying #{ip}"
    res = `ping -c1 -t1 #{ip}`
    if res["1 packets received"] then
      puts "#{ip} answered!"
      open("used_ips", "a") do |file|
        file.puts ip
      end
      ips -= [ip]
    end 
  end
  sleep 60 * 10 
end