def random_string(len)
      rand_max = RAND_CHARS.bytesize
      ret = ""
      len.times{ ret << RAND_CHARS[rand(rand_max)] }
      ret
    end
def random_string(len)
      rand_max = RAND_CHARS.bytesize
      ret = ""
      len.times{ ret << RAND_CHARS[rand(rand_max)] }
      ret
    end
Generates a random string of length +len+