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.

2010-07-20 17:22:31

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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 · 617 weeks ago
Thanks kaedenn. I don't know wether it's more portable, but it is shorter and easier to read/memorize.
CodSpirit · 617 weeks 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 · 615 weeks and 6 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?

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