How to redirect stderr and stdout to different files and also display in terminal?

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.

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

@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.