Wait for a process to finish

Question

To wait for any process to finish

Linux:

tail --pid=$pid -f /dev/null

Darwin (requires that $pid has open files):

lsof -p $pid +r 1 &>/dev/null

With timeout (seconds)

Linux:

timeout $timeout tail --pid=$pid -f /dev/null

Darwin (requires that $pid has open files):

lsof -p $pid +r 1m%s -t | grep -qm1 $(date -v+${timeout}S +%s 2>/dev/null || echo INF)

There's no builtin. Use kill -0 in a loop for a workable solution:

anywait(){

    for pid in "$@"; do
        while kill -0 "$pid"; do
            sleep 0.5
        done
    done
}

Or as a simpler oneliner for easy one time usage:

while kill -0 PIDS 2> /dev/null; do sleep 1; done;

As noted by several commentators, if you want to wait for processes that you do not have the privilege to send signals to, you have find some other way to detect if the process is running to replace the kill -0 $pid call. On Linux, test -d "/proc/$pid" works, on other systems you might have to use pgrep (if available) or something like ps | grep "^$pid ".

I found "kill -0" does not work if the process is owned by root (or other), so I used pgrep and came up with:

while pgrep -u root process_name > /dev/null; do sleep 1; done

This would have the disadvantage of probably matching zombie processes.

This bash script loop ends if the process does not exist, or it's a zombie.

PID=<pid to watch>
while s=`ps -p $PID -o s=` && [[ "$s" && "$s" != 'Z' ]]; do
    sleep 1
done

EDIT: The above script was given below by Rockallite. Thanks!

My orignal answer below works for Linux, relying on procfs i.e. /proc/. I don't know its portability:

while [[ ( -d /proc/$PID ) && ( -z `grep zombie /proc/$PID/status` ) ]]; do
    sleep 1
done

It's not limited to shell, but OS's themselves do not have system calls to watch non-child process termination.

FreeBSD and Solaris have this handy pwait(1) utility, which does exactly, what you want.

I believe, other modern OSes also have the necessary system calls too (MacOS, for example, implements BSD's kqueue), but not all make it available from command-line.