How to monitor and alert on Write rendering

Local rendering can be monitored using the following bash script. This will send an email when the render finishes or fails. It checks the Natron write process every 90 seconds.

#!/bin/bash
echo -e "Testing Natron -b -w \nStarted at $(date +"%T")"
while true;
do
    ps ax | grep "Natron -b -w" | grep -v grep &> /dev/null

    if [ $? == 1 ]; then
        echo "Natron stopped at $(date +"%T")"
        echo "" | mail -s "Natron stopped" email@address
    fi
    sleep 90;
done