"2>&1" 是什么意思?[重定向问题合并]

lordbyorn

Of cause you can redirect stdout and stderr like this:
command &>filename.
But this is not so good.
You will see that the messages from stderr and stdout may cross into each other.
Why? Caz stderr is non-bufferred output, while stdout is bufferred output.
So type  command>filename 2 >&1 will be better.
But if you type  command>filename 1 >&2 will get the some effect as command &>filename

2. We assume the x corrdinate is time zone
3. When we type command &>filename, the stream is like this
4. Caz, non-buffered output is slow.
5. V y
6. |
7. | s        t          d           e          r          r
8. |  stdout
9. |
10. |                                                                         x
11. |---------------------------------------------------------->(time)
12. So you see that stderr and stdout cross into each other.
14. But while you type like command>filename 2 >&1
15. the stream is like this,Caz, buffered output is fast.
16. |
17. |                   stderr
18. |  stdout
19. |
20. |                                                                         x
21. |---------------------------------------------------------->(time)
22. So this is good.

复制代码

Of cause I left out some other things.

If my understanding is wrong, please correct it.

KornLee

给楼主一个咱们版以前关于重定向的讨论的铁子,(中文的);)
http://www.linuxsir.cn/bbs/showt ... =%D6%D8%B6%A8%CF%F2
另外,在我们提问之前,建议先搜索一下论坛,有很多问题都是可以找到解决方案的!

lordbyorn

So some of understanding is wrong.

I should read more book.

But how about this?:
command &>file

How to produce stderr output in shell?

ft, wrong place!!

lordbyorn

So some of understanding is wrong.

I should read more book.

But how about this?:
command &>file

How to produce stderr output in shell?

Glue

&>file 等同于 >file 2>&1
还有一种写法是 >& file，但不正规。
这是 man bash 里说的。

lordbyorn

so &> eq >& ,right?

Andyou think my understanding is wrong or not?

NetDC

最初由 javalee 发表
给楼主一个咱们版以前关于重定向的讨论的铁子,(中文的);)
http://www.linuxsir.cn/bbs/showt ... =%D6%D8%B6%A8%CF%F2
另外,在我们提问之前,建议先搜索一下论坛,有很多问题都是可以找到解决方案的!

明白了，不过为什么上面这篇没加到精华呢？

Glue

最初由 lordbyorn 发表
so &> eq >& ,right?

Andyou think my understanding is wrong or not?

yes,
but &> is preferred.

from "man bash"

       There  are  two  formats  for  redirecting standard output and standard
       error:

              &>word
       and
              >&word

       Of the two forms, the first is preferred.  This is semantically equiva-
       lent to

              >word 2>&1