Shell function to tail a log file for a specific string for a specific time

Question

I need to the following things to make sure my application server is

1. Tail a log file for a specific string
2. Remain blocked until that string is printe

Answer 1

You can use signal handlers from shell scripts (see http://www.ibm.com/developerworks/aix/library/au-usingtraps/index.html).

Basically, you'd define a function to be called on, say, signal 17, then put a sub-script in the background that will send that signal at some later time:

timeout(pid) {
   sleep 1200
   kill -SIGUSR1 $pid
}

watch_for_input() {
   tail -f file | grep item
}

trap 'echo "Not found"; exit' SIGUSR1
timeout($$) &
watch_for_input

Then if you reach 1200 seconds, your function is called and you can choose what to do (like signal your tail/grep combo that is watching for your pattern in order to kill it)