文件描述符 [英] File descriptors

问题描述

有人能告诉我为什么不起作用？我玩弄文件描述符，反而觉得有点失落。

Can some one tell me why this does not work? I'm playing around with file descriptors, but feel a little lost.

#!/bin/bash
echo "This"
echo "is" >&2
echo "a" >&3
echo "test." >&4

前三行运行良好，但最后两个错误的。为什么？感谢您的帮助！

The first three lines run fine, but the last two error out. Why? Thanks for the help!

推荐答案

文件描述符0，1和2分别是标准输入，输出和错误。

File descriptors 0, 1 and 2 are for stdin, stdout and stderr respectively.

文件描述符3，4，9 ..对于其他文件。为了使用它们，你需要先打开它们。例如：

File descriptors 3, 4, .. 9 are for additional files. In order to use them, you need to open them first. For example:

exec 3<> /tmp/foo  #open fd 3.
echo "test" >&3
exec 3>&- #close fd 3.

有关详细信息，看一看高级Bash脚本编程指南：第20章I / O重定向

For more information take a look at Advanced Bash-Scripting Guide: Chapter 20. I/O Redirection.

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