tee to a file descriptor

tee >(cat - >&2)

the tee command does fine with file names, but not so much with file descriptors, such as &2 (stderr). This uses process redirection to tee to the specified descriptor. In the sample output, it's being used to tee to stderr, which is connected with the terminal, and to wc -l, which is also outputting to the terminal. The result is the output of bash --version followed by the linecount

Sample Output

$ bash --version |tee  >(cat - >&2) | wc -l
GNU bash, version 3.2.49(1)-release (i586-suse-linux-gnu)
Copyright (C) 2007 Free Software Foundation, Inc.
2

By: camocrazed

2010-07-20 17:22:31

cat tee cat tee redirection file descriptor

1 Alternatives + Submit Alt

Use tee to process a pipe with two or more processes

Tee can be used to split a pipe into multiple streams for one or more process to work it. You can add more " >()" for even more fun. Show Sample Output
This is sample output - yours may be different.
```
tee can split a pipe in two
tee_can_split_a_pipe_in_two
owt ni epip a tilps nac eet
```
34

echo "tee can split a pipe in two"|tee >(rev) >(tr ' ' '_')

axelabs · 2010-08-14 20:38:59 10

What Others Think

This screams of a bash high-level usage of dup2(). I love it. This means I can "redirect" stdout to both stdout and stderr. But wouldn't tee /dev/stderr do the same thing, in a way that's a little more portable?

kaedenn · 741 weeks and 3 days ago

Thanks kaedenn. I don't know wether it's more portable, but it is shorter and easier to read/memorize.

CodSpirit · 741 weeks and 2 days ago

I think you're right there kaedenn, but then you're limited to the three regular ones that are duplicated in /dev, whereas the >(...) is resolved to a numerically named file in the /dev/fd directory, which gives you a few more options. More reading here: http://www.gnu.org/software/bash/manual/bashref.html#Redirections Also, if you want to do some further processing, you sort of need to use the process substitution method anyways. For example: echo "foo" |tee >(sed 's/.*/& 2/' >&2)| sed 's/.*/& 1/' should output a 2 next to the stderr copy, and a 1 next to the stdout copy. I'm not sure how you would do that using a write only file like /dev/stderr

camocrazed · 740 weeks and 2 days ago

rahimhh21 · 109 weeks and 3 days ago

Perfecthomepugs · 100 weeks and 4 days ago

pugpuppies95 · 62 weeks and 5 days ago

yeneba6574 · 17 weeks and 4 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

You must be signed in to comment.

What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

Share Your Commands

Similar Commands

save stderr only to a file

truncate file descriptor

Read and write to TCP or UDP sockets with common bash tools

Play files with mplayer, including files in sub-directories, and have keyboard shortcuts work

Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10

Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for:

» all commands
» commands with 3 up-votes (commandlinefu3)
» commands with 10 up-votes (commandlinefu10)