reverse_read.rb

def testing_seek(filename)
  return nil if File.size(filename) < 3

  File.open(filename, 'rb') do |fd|
    buffer = "".b
    fd.seek(-1, IO::SEEK_END)

    until fd.pos.zero? || buffer[0, 3] == '---'
      buffer = fd.read(1) + buffer
      fd.seek(-2, IO::SEEK_CUR)
    end

    buffer[0, 3] == '---' ? buffer : nil
  end
end