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Accepted
AntonioK
Asked: 2023-08-22 14:06:07 +0800 CST

Send STDERR to console and file, STDOUT to file only

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I have some script with STDOUT and STDERR output. By default, both STDOUT and STDERR goes to console:

./script.sh

I can redirect STDOUT to file, leaving STDERR output in console:

./script.sh > log.txt

I can redirect both STDOUT + STDERR to same file with no output in console:

./script.sh > log.txt 2>&1

I can have both STDOUT and STDERR in console and logfile simultaneously:

./script.sh 2>&1 | tee -a log.txt

I don't want to see STDOUT, but I want to see STDERR, and I have to save everything in logfile. How could I have STDERR in console + logfile, while STDOUT in logfile only? Something like (pseudo-code, doesn't work):

./script.sh > log.txt 2 > /dev/tty | tee -a log.txt
linux

1 Answers

  1. Best Answer

    You would have to append both STDERR & STDOUT to the file. Otherwise the other of the streams would write over the other.

    ./script.sh >> log.txt 2> >(tee -a log.txt >&2)

    Where:

    1. >> log.txt appends STDOUT to log.txt.
    2. 2> > sends the STDERR to to be processed by (tee -a log.txt >&2).
    3. tee -a log.txt splits that to the file log.txt in append (-a) mode and to >&2.
    4. As the STDERR was temporarily sent to STDOUT, the >&2 puts it back to STDERR.

    Considerations

    Because of the appending, if you run this twice, you would have the output twice in the file – which I suppose is the goal, given it is a log file. If you would like to have only the latest run in the log file, you would have to empty it first, e.g.,

    > log.txt && ./script.sh >> log.txt 2> >(tee -a log.txt >&2)

    The lines would not appear in chronological order, as >> works a bit faster tee -a. Because the latter has to fork another process, the output from STDERR would come to the file with a delay. If the correct order is critical, you cannot use this solution.

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