daemon.rb

class Daemon
  def self.run &block
    new &block
  end

  def initialize &block
    Process.daemon
    @pid = Process.pid
    File.write '/tmp/daemon.pid', @pid
    yield
  end
end


Daemon.run do
  file = File.new('/tmp/daemon.log', 'a')
  count = 0
  loop { file.write "#{count += 1}\n" }
end