29

I want to see the output of a command in the terminal as if there was no redirection. Also, stderr needs to be redirected to err.log and stdout needs to be redirected to stdout.log.

It would be nice to also have the exact copy of what is shown in terminal, i.e. errors printed as and when it occurs, in a separate file: stdouterr.log.

37

Use the tee command as follows:

(cmd | tee stdout.log) 3>&1 1>&2 2>&3 | tee stderr.log

3>&1 1>&2 2>&3 is how you swap stderr and stdout, because tee can only accept stdout.

Take a look at Unix tee command for more advanced redirections using tee.

  • nice solution. Is there any way to get cmd exit code? – turbanoff Jun 19 '15 at 16:56
  • 2
    @turbanoff Replace cmd with (cmd ; echo >exit_code.txt $?). – Parthian Shot Aug 13 '15 at 21:04
  • I believe this should better-preserve the order of things output to the command line: ((cmd | tee stdout.log) 3>&1 1>&2 2>&3 | tee stderr.log) – TTT May 7 at 17:12
5

I think logging stdout and stderr to two different files is a splendid idea. Does it not make the logs asynchronous? So I tried out the following:

  • stdout to "stdout.log" (as dogbane suggested)
  • stderror to "stderr.log" (as dogbane suggested)
  • all output to "all.log" and
  • still be able to see the output on the display (in a separate terminal though!)

((cmd | tee stdout.log) 3>&1 1>&2 2>&3 | tee stderr.log) &> all.log

in another terminal

tail -f --sleep-interval=2 all.log
  • Is it not possible to direct stderr directly to a second tty? Then no logfile is required. – Steven Lu Apr 25 '13 at 18:40
  • @StevenLu yes, if you know the name and have permission to write to the second tty that can be done. – Jasen Dec 14 '15 at 23:46
  • 1
    easier would be &| tee all.log on the end of the command instead of &> all.log – Jasen Dec 14 '15 at 23:49
  • @Jasen: 2nd time I see &| . I understand &>, |& too, but what does &| mean in this context ? I could not find a suitable syntax reference, not on the net, not even consulting the bash manual page "bash(1)"... Tx – Cbhihe Feb 7 '16 at 16:25
  • 1
    @Cbhihe as far as I can tell it does nothing, I meant to say |& – Jasen Feb 7 '16 at 19:05
3

@dogbane, Thanks.
I found another way too which saves both the streams approximately in the order as they would get printed without redirection.

command 2> >(tee errlog | tee -a bothLog > /dev/tty ) | tee outlog | tee -a bothLog

But this works only with the shells which supports process substitution.

-2

try this :

command 2>&1 | tee bothLog
  • 4
    Hello vasile, this doesn't answer the question: balki needs separate files for stdout and stderr, your solution would mix both in the same stream. – Mat Nov 1 '12 at 10:45
  • Why do people merge stdout and stderr together? Or tell others to do so? – nurettin Oct 7 '18 at 10:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.