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user4002112
Asked: 2020-04-09 19:35:01 +0800 CST

How to redirect the output of a command to a function but suppress the error and output to console?

  • 772

I need to redirect the output of a command that I am running to a log file with timestamp (hence a function instead of the log file itself) but the error and the output, both should not be showing in the console. The following -

command | my_func 2> /dev/null

is not working.

Something like

command 2> logfile

works, but I can't record the timestamp in the second case. What should I do?

bash error-handling timestamp stdout

4 Answers

  1. It seems you want:

    command 2> /dev/null | my_func

    which redirects the stderr of command to /dev/null, but pipes stdout to my_func. (Side note: You might want to check out the ts command).

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  2. Best Answer

    You do not even need a function for that!

    To redirect errors to /dev/null and output to a file with time and date, you could use sed like so:

    command 2> /dev/null | sed -e "s/^/$(date) /" >> logfile

    sed -e "s/^/$(date) /" will append the current date in this format Thu 09 Apr 2020 07:06:14 AM +03 to the beginning of each line and add a space between the date and the output for readability purposes.

    Notice:

    • To redirect both error and output to a file with time and date, use this:
    command 2>&1 | sed -e "s/^/$(date) /" >> logfile
    • To use timestamp in seconds since the Unix epoch like this 1586406740. change $(date) to $(date +%s)

    Best of luck

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  3. If a timestamp is all that is needed see ts from the moreutils package.

    command | ts

$ sudo apt install moreutils
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  4. Another option is to use GNU awk:

    myprogram | gawk '{print strftime(), $0}' >> logfile

    If you also want to log standard error (assumes bash shell):

    myprogram |& gawk '{print strftime(), $0}' >> logfile
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