auto shutdown when low battery

autodown.rb

#!/usr/bin/ruby

IO.popen("sudo -Hs", "r+") do |sudo|
  
  sudo.puts "echo login_test"
  testmes = sudo.gets
  if testmes != "login_test\n"
    break
  end
  
  while true
    
    percent = nil
    
    IO.popen("upower -i /org/freedesktop/UPower/devices/battery_BAT0", "r") do |io|
      while line = io.gets
        if line =~ /percentage:\s+([^%]+)%/
          percent = $1.to_f
        end
      end
      $stderr.puts percent
    end
    
    if percent < 30
      puts "-------- going to shutdown ---------"
      sudo.puts 'shutdown -h now'
      break
    end
    
    sleep 10
    
  end
  

end