Pipe and watch piped output?

Question

I want to make a shell-pipe like this:

producer | analyser > report.txt

and watch the output of producer while it is generating data (a big log-file) for analysis.

How can I do that?

reinierpost · Accepted Answer · 2012-02-10T12:23:36.440

5

In /bin/sh and compatibles:

producer | tee /dev/fd/3 | (analyser > report.txt) 3>&1

I've tested this only on Linux and Cygwin. On some Unix-likes you may have to change /dev/fd/3 to whatever their equivalent is.

edited Feb 10 '12 at 12:23

answered Feb 10 '12 at 12:11

reinierpost

that will show and save the output of analyser, right? I want to see the output of producer. – Bastl Feb 10 '12 at 12:12
sorry - better now? – reinierpost Feb 10 '12 at 12:14
That will save producer's output to report.txt and I'd have to watch it using "tail -F". Not exactly what I wanted... – Bastl Feb 10 '12 at 12:16
Fixed once again. I should learn to actually read stuff before replying. – reinierpost Feb 10 '12 at 12:25
1

On Ubuntu, I had to use /dev/fd/2 for stdout. Thanks! – Bastl Feb 10 '12 at 13:33
Trying to understand /dev/fd/3, I believe to have learned that 3 isn't defined, and therefore doesn't work everywhere, while /dev/fd/2 sends the output to stderr, which isn't sent into the pipe by default. – not2savvy Dec 10 '22 at 14:48
Indeed, numbers 3 and up don't exist by default. Try running sh -c 'echo hello 1>&3 && ls -l /dev/fd/' 3>&1 and you will see /dev/fd/3. – reinierpost Dec 10 '22 at 18:56

1 Answers1