CLI: Job Control in ZSH and Bash

job_control_zsh_bash.md

Job Control in ZSH and Bash

All processes in ZSH/Bash under job control are in 3 states: foregrounded, backgrounded and suspended.

# run command in the foreground
command
# run commend in the background
command &
# show the list of jobs ([job-id] priority status command) 
jobs

Once we are running the command, we can suspend by sending the SIGTSTP signal using the keyboard:

Ctrl + Z

It will return us to the shell. At this point can do a few things (note that kill is the shell built in kill not the unix kill, which can be accessed via command kill ):

# foreground the job 1 (return it to the foreground)
fg %1
# background the job 2 (make it continue in the background)
bg %2
# kill the job 3 (sends SIGTERM, not like Ctrl + C which sends SIGINT)
kill %3
# suspend the job 4 (equal to Ctrl + Z)
kill -TSTP %4
# continue the job 5 (equal to bg %5)
kill -CONT %5
# show all running jobs
jobs -r
# show all stopped jobs
jobs -s
# show all jobs
jobs
# show all jobs with process ids
jobs -l
# show all jobs with process group ids
jobs -p
# only in ZSH, show all jobs with the directory the started in
jobs -d
# show status about 1 job
jobs %6
# the above flags can be combined to filter for specific jobs

Or (using prefix search), which only works with fg or bg, but not kill:

fg %command
bg %command

There are some shortcuts like:

# foreground the most recent backgrounded job
%
# same thing as above
%+
# foreground the second most recent backgrounded job
%-

But for best portability across commands, use the job numbers %n where n is the job number.

In ZSH, if you use try to suspend a function operation, it will fork the shell. That function will now be in a totally different process, so any mutation side effects will not be reflected in your shell. This is good of course, because functions should be pure.

To send a signal to all jobs, or kill all of them, use this function:

: '
killjobs - Run kill on all jobs in a Bash or ZSH shell, allowing one to optionally pass in kill parameters

Usage: killjobs [zsh-kill-options | bash-kill-options]

With no options, it sends `SIGTERM` to all jobs.
'
killjobs () {

    local kill_list="$(jobs)"
    if [ -n "$kill_list" ]; then
        # this runs the shell builtin kill, not unix kill, otherwise jobspecs cannot be killed
        # the `$@` list must not be quoted to allow one to pass any number parameters into the kill
        # the kill list must not be quoted to allow the shell builtin kill to recognise them as jobspec parameters
        kill $@ $(sed --regexp-extended --quiet 's/\[([[:digit:]]+)\].*/%\1/gp' <<< "$kill_list" | tr '\n' ' ')
    else
        return 0
    fi

}

This is a good reference. May I suggest also disown to remove a process from the job control list. Can be useful sometimes.

Works fine with Bash, but it doesn't work with ZSH. That's because killjobs function is treated like a separate process when it's been invoked. So there aren't any jobs for builtin-jobs command to show. In ZSH builtin jobs implementation is slightly different (and worse).