文件描述符如何工作? [英] How do file descriptors work?

问题描述

有人可以告诉我为什么这行不通吗?我在玩文件描述符，但是有点迷路.

Can someone 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

前三行运行正常，但后两行出错.为什么?

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

推荐答案

文件描述符0、1和2分别用于stdin，stdout和stderr.

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

文件描述符3、4，.. 9用于附加文件.为了使用它们，您需要先打开它们.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.

有关更多信息，请参见高级Bash脚本指南: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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