使用 tee 重定向文件描述符 3
我几个月前写了这个脚本，现在重读它，我无法解读这行代码的含义：
sudo rsync -xPRSaz --rsync-path='sudo rsync' maeve@macbook:/ macbook/ 3>&1 1>&2 2>&3 | tee macbook.log
我找不到对 sudo, 文件描述符 3 的任何特殊处理>rsync 或 tee。重定向之后，我目前猜测情况是这样的：
now fd points to old fd
0 --> 0
1 --> 2
2 --> 1
3 --> 1
- 这些重定向是否应用于 sudo 或 rsync，目的是什么？
- 文件描述符 3 是否未关闭或以任何“不良”方式挂起？
I wrote this script some months ago, and now rereading it, I'm unable to decipher what I meant by this line:
sudo rsync -xPRSaz --rsync-path='sudo rsync' maeve@macbook:/ macbook/ 3>&1 1>&2 2>&3 | tee macbook.log
I can't find any special treatment of file descriptor 3 for sudo, rsync or tee. After the redirects I'm currently guessing this is the situation:
now fd points to old fd
0 --> 0
1 --> 2
2 --> 1
3 --> 1
- Are these redirects applied to
sudo, or torsync, and to what end? - Is file descriptor 3 being left unclosed or hanging in any "bad" way?
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你的猜测是对的。交换标准输出和标准错误是一个相当巧妙的技巧。回答您的问题：
sudo）。sudo进程本身将检测所有参数并将它们传递给其子命令 (rsync)，但在此之前重定向已被捕获并执行操作：sudo从未见过他们。Your guess is right. It's a rather nifty trick to swap standard output and standard error. To answer your questions:
sudo). Thesudoprocess itself will detect all the arguments and pass them along to its subcommand (rsync) but the redirections have been captured and acted upon before that point:sudonever sees them.请注意，悬空文件描述符
3可以使用3>&-关闭，以下是包含的完整行：Note that the dangling file descriptor
3can be closed with3>&-, here's the full line with that included: