有一个命令叫做 yes ， 它默认是不断的写 y 到 stdout 上，在被杀掉之前呢，它会一直喋喋不休的啦～
很简单，要说这个东西想实现也很简单，但是我找到源码，让我自己看起来却没那么轻松……（毕竟主要的功能的确很简单，但是命令行参数的处理，还有文档，还有man这些的我是一点都不了解怎么作阿;p）
不过用

$yes > somefile.name

这样生成一个文件再压缩一下发给别人还是很要命的。

这样一来，几秒钟可以生成几百兆的文件，但是因为内容都一直，所以一压缩也就基本没什么东西了。比如我生成了一个将近 700MB 的文件压缩之后只有600多KB 然后某人解压缩的时候，电脑死机了。。哈哈 当然死机的原因是多方面的，主要还是机器太老的缘故哦？

这些都是在论坛讨论 出来的结果阿～～ 哈哈。。。
源码贴在这里，慢慢学习：

/* yes - output a string repeatedly until killed
   Copyright (C) 1991-1997, 1999-2004, 2007-2010 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

/* David MacKenzie <djm@gnu.ai.mit.edu> */

#include <config.h>
#include <stdio.h>
#include <sys/types.h>
#include <getopt.h>

#include "system.h"

#include "error.h"
#include "long-options.h"

/* The official name of this program (e.g., no `g' prefix).  */
#define PROGRAM_NAME "yes"

#define AUTHORS proper_name ("David MacKenzie")

void
usage (int status)
{
  if (status != EXIT_SUCCESS)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
             program_name);
  else
    {
      printf (_("\
Usage: %s [STRING]...\n\
  or:  %s OPTION\n\
"),
              program_name, program_name);

      fputs (_("\
Repeatedly output a line with all specified STRING(s), or `y'.\n\
\n\
"), stdout);
      fputs (HELP_OPTION_DESCRIPTION, stdout);
      fputs (VERSION_OPTION_DESCRIPTION, stdout);
      emit_ancillary_info ();
    }
  exit (status);
}

int
main (int argc, char **argv)
{
  initialize_main (&argc, &argv);
  set_program_name (argv[0]);
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  atexit (close_stdout);

  parse_long_options (argc, argv, PROGRAM_NAME, PACKAGE_NAME, Version,
                      usage, AUTHORS, (char const *) NULL);
  if (getopt_long (argc, argv, "+", NULL, NULL) != -1)
    usage (EXIT_FAILURE);

  if (argc <= optind)
    {
      optind = argc;
      argv[argc++] = bad_cast ("y");
    }

  for (;;)
    {
      int i;
      for (i = optind; i < argc; i++)
        if (fputs (argv[i], stdout) == EOF
            || putchar (i == argc - 1 ? '\n' : ' ') == EOF)
          {
            error (0, errno, _("standard output"));
            exit (EXIT_FAILURE);
          }
    }
}