在 shell 中，什么是 "2>&1"意思? [英] In the shell, what does " 2>&1 " mean?

问题描述

在 Unix shell 中，如果我想将 stderr 和 stdout 组合到 stdout 流中以进行进一步操作，我可以附加以下内容在我的命令结束时:

In a Unix shell, if I want to combine stderr and stdout into the stdout stream for further manipulation, I can append the following on the end of my command:

2>&1

所以，如果我想在 g++ 的输出上使用 head，我可以这样做:

So, if I want to use head on the output from g++, I can do something like this:

g++ lots_of_errors 2>&1 | head

所以我只能看到前几个错误.

so I can see only the first few errors.

我总是很难记住这一点，我不得不经常去查，这主要是因为我不完全理解这个特殊技巧的语法.

I always have trouble remembering this, and I constantly have to go look it up, and it is mainly because I don't fully understand the syntax of this particular trick.

有人可以分解一下并逐个解释 2>&1 是什么意思吗?

Can someone break this up and explain character by character what 2>&1 means?

推荐答案

文件描述符 1 是标准输出 (stdout).
文件描述符 2 是标准错误 (stderr).

File descriptor 1 is the standard output (stdout).
File descriptor 2 is the standard error (stderr).

这是记住这个结构的一种方法(尽管它并不完全准确):起初，2>1 可能看起来是一种将 stderr 重定向到的好方法标准输出.但是，它实际上会被解释为将 stderr 重定向到名为 1 的文件".& 表示后面和前面的是文件描述符而不是文件名.所以构造变成:2>&1.

Here is one way to remember this construct (although it is not entirely accurate): at first, 2>1 may look like a good way to redirect stderr to stdout. However, it will actually be interpreted as "redirect stderr to a file named 1". & indicates that what follows and precedes is a file descriptor and not a filename. So the construct becomes: 2>&1.

将 >& 视为重定向合并运算符.

Consider >& as redirect merger operator.

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