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shaneoh
Asked: 2017-11-29 01:13:46 +0800 CST

Direct output from a command to a file including the original command, AND print in terminal

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When running some tests, I need to run a series of commands. It would be extremely useful to me, and save me a lot of time, if there was a way to do all of these things:

  • Run the command I need to run
  • Redirect all the output from the command to a specified file
  • Include the original command in the specified file
  • Print the output from the original command in the terminal

People have suggested using tee to me which does a great job of printing to terminal as well as sending to a file but doesn't include the original command. What I'd like to end up with is a file where the first line is the command I ran, and then below that is the output from the command.

Someone suggested this:

echo "ls -l" | xargs -I{} bash -c "echo >> output.file; eval {} >> output.file"

But this doesn't either print the output in the terminal or include the original command in the file.

I'd appreciate any ideas.

command-line

3 Answers

  1. Best Answer

    That's tee you're searching for.

    ls -l | tee outfile

    prints the output of ls -l to stdout (i.e. the terminal) and saves it in the file outfile at the same time. But: It doesn't write the command name neither to stdout nor to the file. To achieve that, just echo the command name before running the command and pipe both outputs to tee:

    ( echo "ls -l" && ls -l ) | tee outfile

    That's cumbersome to type, so why not define a function?

    both(){ ( echo "$@" && "$@" ) | tee outfile ;}

    After that you can just run

    both ls -l

    to get the desired result. Put the function in your ~/.bashrc to have it defined in every new terminal.

    If you want to be able to specify the output file as the first argument like in

    both output ls -l

    instead make it:

    both(){ ( echo "${@:2}" && "${@:2}" ) | tee "$1" ;}

    If you don't want the output file to be overwritten but rather append to it, add the -a option to tee.

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  2. You could make use of the script command which will make a typescript file of everything printed to your terminal. It creates a forked shells and will record everything until that shell is exited.

    $ script my_output
Script started on Tue 28 Nov 2017 09:46:15 AM UTC
$ whoami
ajefferiss
$ exit
Script done on Tue 28 Nov 2017 09:46:27 AM UTC

    Then if I cat my_output I get the same output:

    $ cat my_output
Script started on Tue 28 Nov 2017 09:46:15 AM UTC
$ whoami
ajefferiss
$ exit
exit

Script done on Tue 28 Nov 2017 09:46:27 AM UTC
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  3. You can use the debugging function of the shell together with tee:

    ( set -x; command1 args...; command2 args ) 2>&1 | tee output.log

    • ( ... ) starts a sub-shell which allows you to “collect” the output streams of all commands executed within the sub-shell. It also contains the effect of the set command below to this sub-shell.

    • set -x enables the x shell option which prints all commands that the shell runs to the standard error stream before running them.

    • 2>&1 redirects stream 2 (standard error) to stream 1 (standard output).

    • | redirects the the standard output stream of the left command to the standard input stream of the right command.

    • tee FILE copies the standard input stream to the file FILE and to standard output.

    If your command sequence is already in a script file it would make more sense to run it like this:

    bash -x /path/to/script args... 2>&1 | tee output.log
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