Is there a way to redirect standard error to the input of another command (BASH / RHE4)?
I can send it to a file, grep the file for what I need, then delete the file, but this method seems a bit sloppy.

Is there a more efficient way to do it?
(I tried redirecting stderr to stdout, then greping for what I need, but stdout occasionally includes text that fowls up my grep sequence.)

Thanks!

You should be able to just swap the file descriptors for stdout
and stderr if stderr is all you need to post-process...


Cheers,
Tink

Tinkster taught me a way to put everything in one line because I used to do : exec 3>&1 ... cmd1 | cmd2

Actually, it is an interesting question and also a good practice. I explored a little bit and found that if you want stdout of cmd1 to disappear and only stderr of cmd1 piped into cmd2 without being displayed, you can do the following:

I wrote a sample script for testing:
#!/bin/bash
echo "output for stdout" >&1
echo "output for stderr" >&2
exit 0

$ (./a_cmd.sh | wc -l) 3>&1 1>&2 2>&3
output for stderr
1

$ (./a_cmd.sh | wc -l) 3>&1 1>/dev/null 2>&1 1>&3
1

Tinkster, the above works but I don't know how it works. Can you explain? Thanks.

Maybe I'm more of a no0b than you realize: I know "1" is stdout and "2" is stderr, but what's the "3" mean? Stdout and stderr combined?

Like IlTux above, I can plug different commands into the formula and get different results, but I don't know what's really happening to generate the differences.

It’s just a placeholder file descriptor. See man exec.