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Functions

tee to a file descriptor

Terminal - tee to a file descriptor
tee >(cat - >&2)
2010-07-20 17:22:31
User: camocrazed
Functions: cat tee
5
tee to a file descriptor

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

Alternatives

There are 2 alternatives - vote for the best!

Terminal - Alternatives
echo "tee can split a pipe in two"|tee >(rev) >(tr ' ' '_')
2010-08-14 20:38:59
User: axelabs
Functions: echo tee tr
33

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.

Know a better way?

If you can do better, submit your command here.

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?

Comment by kaedenn 226 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.

Comment by CodSpirit 226 weeks and 3 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

Comment by camocrazed 225 weeks and 2 days ago

Your point of view

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