Bash Commands – Run Multiple Commands and Kill Them as One in Bash

background-processbashcommand lineprocessprocess-groups

I want to run multiple commands (processes) on a single shell. All of them have own continuous output and don't stop. Running them in the background breaks Ctrl–C. I would like to run them as a single process (subshell, maybe?) to be able to stop all of them with Ctrl–C.

To be specific, I want to run unit tests with mocha (watch mode), run server and run some file preprocessing (watch mode) and see output of each in one terminal window. Basically I want to avoid using some task runner.

I can realize it by running processes in the background (&), but then I have to put them into the foreground to stop them. I would like to have a process to wrap them and when I stop the process it stops its 'children'.

Best Answer

To run commands concurrently you can use the & command separator.

~$ command1 & command2 & command3

This will start command1, then runs it in the background. The same with command2. Then it starts command3 normally.

The output of all commands will be garbled together, but if that is not a problem for you, that would be the solution.

If you want to have a separate look at the output later, you can pipe the output of each command into tee, which lets you specify a file to mirror the output to.

~$ command1 | tee 1.log & command2 | tee 2.log & command3 | tee 3.log

The output will probably be very messy. To counter that, you could give the output of every command a prefix using sed.

~$ echo 'Output of command 1' | sed -e 's/^/[Command1] /' 
[Command1] Output of command 1

So if we put all of that together we get:

~$ command1 | tee 1.log | sed -e 's/^/[Command1] /' & command2 | tee 2.log | sed -e 's/^/[Command2] /' & command3 | tee 3.log | sed -e 's/^/[Command3] /'
[Command1] Starting command1
[Command2] Starting command2
[Command1] Finished
[Command3] Starting command3

This is a highly idealized version of what you are probably going to see. But its the best I can think of right now.

If you want to stop all of them at once, you can use the build in trap.

~$ trap 'kill %1; kill %2' SIGINT
~$ command1 & command2 & command3

This will execute command1 and command2 in the background and command3 in the foreground, which lets you kill it with Ctrl+C.

When you kill the last process with Ctrl+C the kill %1; kill %2 commands are executed, because we connected their execution with the reception of an INTerupt SIGnal, the thing sent by pressing Ctrl+C.

They respectively kill the 1st and 2nd background process (your command1 and command2). Don't forget to remove the trap, after you're finished with your commands using trap - SIGINT.

Complete monster of a command:

~$ trap 'kill %1; kill %2' SIGINT
~$ command1 | tee 1.log | sed -e 's/^/[Command1] /' & command2 | tee 2.log | sed -e 's/^/[Command2] /' & command3 | tee 3.log | sed -e 's/^/[Command3] /'

You could, of course, have a look at screen. It lets you split your console into as many separate consoles as you want. So you can monitor all commands separately, but at the same time.

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