How do I limit the running time of a BASH script

Question

I have a long running BASH script that I am running under CYGWIN on Windows.

I would like to limit the script to run for 30 seconds, and automatically terminate if i

Answer 1

The following script shows how to do this using background tasks. The first section kills a 60-second process after the 10-second limit. The second attempts to kill a process that's already exited. Keep in mind that, if you set your timeout really high, the process IDs may roll over and you'll kill the wrong process but this is more of a theoretical issue - the timeout would have to be very large and you would have to be starting a lot of processes.

#!/usr/bin/bash

sleep 60 &
pid=$!
sleep 10
kill -9 $pid

sleep 3 &
pid=$!
sleep 10
kill -9 $pid

Here's the output on my Cygwin box:

$ ./limit10
./limit10: line 9:  4492 Killed sleep 60
./limit10: line 11: kill: (4560) - No such process

If you want to only wait until the process has finished, you need to enter a loop and check. This is slightly less accurate since sleep 1 and the other commands will actually take more than one second (but not much more). Use this script to replace the second section above (the "echo $proc" and "date" commands are for debugging, I wouldn't expect to have them in the final solution).

#!/usr/bin/bash

date
sleep 3 &
pid=$!
((lim = 10))
while [[ $lim -gt 0 ]] ; do
    sleep 1
    proc=$(ps -ef | awk -v pid=$pid '$2==pid{print}{}')
    echo $proc
    ((lim = lim - 1))
    if [[ -z "$proc" ]] ; then
            ((lim = -9))
    fi
done
date
if [[ $lim -gt -9 ]] ; then
    kill -9 $pid
fi
date

It basically loops, checking if the process is still running every second. If not, it exits the loop with a special value to not try and kill the child. Otherwise it times out and does kill the child.

Here's the output for a sleep 3:

Mon Feb  9 11:10:37 WADT 2009
pax 4268 2476 con 11:10:37 /usr/bin/sleep
pax 4268 2476 con 11:10:37 /usr/bin/sleep
Mon Feb  9 11:10:41 WADT 2009
Mon Feb  9 11:10:41 WADT 2009

and a sleep 60:

Mon Feb  9 11:11:51 WADT 2009
pax 4176 2600 con 11:11:51 /usr/bin/sleep
pax 4176 2600 con 11:11:51 /usr/bin/sleep
pax 4176 2600 con 11:11:51 /usr/bin/sleep
pax 4176 2600 con 11:11:51 /usr/bin/sleep
pax 4176 2600 con 11:11:51 /usr/bin/sleep
pax 4176 2600 con 11:11:51 /usr/bin/sleep
pax 4176 2600 con 11:11:51 /usr/bin/sleep
pax 4176 2600 con 11:11:51 /usr/bin/sleep
pax 4176 2600 con 11:11:51 /usr/bin/sleep
pax 4176 2600 con 11:11:51 /usr/bin/sleep
Mon Feb  9 11:12:03 WADT 2009
Mon Feb  9 11:12:03 WADT 2009
./limit10: line 20:  4176 Killed sleep 60