How to know when a background task has finished?

[Kris Spander]

Hello experts,

Does anybody know how to determine if a background task is still running from a shell script?

TIA,
Kris

[Vasikaran Venkatesan]

1) Pressing the enter (if the terminal was inactive after the bg job was started) - should say that "Job was Done"
2) ps -ef | grep -v grep | grep

[A. Clay Stephenson · Accepted solution]

The standard method would be to send a kill -s 0 to the process and look at the result.

e.g.

mychild.sh &
CHILDPID=${!}
...
...
...
kill -s 0 ${CHILDPID} 2>/dev/null
STAT=${?}
if [[ ${STAT} -eq 0 ]]
then
echo "Child is still alive"
else
echo "It ain't"
fi

Plan B.
wait ${CHILDPID}

The parent will block until the designated child completes or
wait
the parent will block until all child processes have finished.

Plan C.
Just before the child process exits, have the child send a signal to the parent that the parent traps. This will allow the parent to continue processing asynchronously.

[Ulrich Deiters]

Once you start the background task, the shell variable $! contains its PID. This can be used for automated checking, e.g.,

start_background_task
alive=`jobs -l | grep $! | wc -l`
if [ $alive -ne 1 ]
then
cleanup_after_bg_task
...

[Steven E. Protter]

you can also route the output through mailx -s

nohup scriptname & | mailx -s "job" me@my.net

the email will be delivered at job completion.

SEP