make 2>&1 | tee xxx.log 引发的思考

最新推荐文章于 2024-12-31 13:09:41 发布

freudlv

最新推荐文章于 2024-12-31 13:09:41 发布

阅读量9.5k

点赞数 1

分类专栏： linux相关文章标签： redirect file descriptor output keyboard fold

linux相关专栏收录该内容

12 篇文章

订阅专栏

本文详细解释了Linux系统中stdin, stdout, 和stderr的概念及其区别，并通过实例演示了如何使用这些标准流进行数据重定向。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

Background of this post:

Recently, I always noticed that many guys can't distinguish the meaning among stdin, stdout, and stderr, especially, they always ask the same question as: what does "2>&1" exactly mean?

So, here I want to give a summary of this three things, and of course, I'd like to take this "2>&1" as an example.

-----------------------
Interpretation:

First of all, I want to give out the exact meaning of "2>&1":

2>&1:

0 is stdin. 1 is stdout. 2 is stderr
-------------
There's one way to remember this construct (maybe it is not entirely accurate):
-------------
First of all, 2>1 looks like a very good way to redirect stderr to stdout. but remember, it has a very harmful disadvantage: it may actually be interpreted as "redirect stderr to a file named 1".
-------------
& indicates that what follows is a file descriptor and not a filename. So the construct becomes: 2>&1.
-------------
>& is shell syntax for "fold a file descriptor into another", you can also interprete it as "it is the syntax to redirect a stream to another file descriptor"

So, now, have you got the meaning of what does "2>&1" exact mean? I think you do!

Yes, it's very easy to understand, but what's more, I want to go little deep into this topic.

-----------------------
Furthermore:

Following picture gives a very clear defination of what is stdin stdout and stderr:

# In Linux everything is a file.
# Your hardware is also a file:
* 0 - Input - Keyboard (stdin)
* 1 - Output - Screen (stdout)
* 2 - Error - Screen (stderr)

# For standard output:

Clear enough?

If you still feel confused about this, you can view this page to find more infomation:
http://tldp.org/LDP/abs/html/io-redirection.html

-----------------------
Example:

Finally, I want to give you a example to end this entry(Try to understand it ^_^):

The output of a.out is the following, without the 'STDXXX: ' prefix.

STDERR: stderr output STDOUT: more regular

./a.out 3>&1 1>&2 2>&3 3>&- | sed 's/e/E/g' more regular stderr output

First save stdout as &3 (&1 is duped into 3).
Next send stdout to stderr (&2 is duped into 1).
Send stderr to &3 (stdout) (&3 is duped into 2).
close &3 (&- is duped into 3)

-----------------------
Others:

If you want to know what's the difference between "cmd >file 2>&1" and "cmd >file 2>file", pls refer this post which written by r2007:
http://bbs.chinaunix.net/thread-764727-1-1.html