Return the last line of a File in a O(n) time

file_lastline.rb

class File
  def last_line
    ind = 1
    loop do
      offset = (ind * -80)
      if(offset >= size)
        seek(0, IO::SEEK_SET)
        line = read
        line.chomp!
        return line.split(/\n/, -1).last
      else
        seek(offset, IO::SEEK_END)
        line = read
        if(line =~ /\n.*\n/)
          line.chomp!
          return line.split(/\n/, -1).last
        end
      end
      ind += 1
    end
  end
end