Question

I have this bash script whose job is to monitor a log file for the occurrence of a certain line. When located, the script will send out an email warning and then terminate itself. For some reason, it keeps on running. How can I be sure to terminate bash script below:

#!/bin/sh

tail -n 0 -f output.err | grep --line-buffered "Exception" | while read line
do
    echo "An exception has been detected!" | mail -s "ALERT" [e-mail]
    exit 0
done

Answer 1

You are opening a subshell in the while read and that subshell is who is exiting, not the proper one.

Try before entering the while loop:

SHELLPID=$$

And then in the loop:

kill $SHELLPID
exit 0

Or change your loop to not use a subshell.

Since the parent script is always going to be in the tail -f which never ends I think you have no other choice than killing it from the inner subshell.