Can a shell script wait for a file to change and take action?
Solution 1:
Cheap n' dirty way:
Loop stat -c %Y file and take action when the modification time changes.
Probably better:
Use the inotify cron service to watch for file modification events and run your action:
/path/to/your/file IN_MODIFY /path/to/your/script $#
Solution 2:
Take a look at incron[1] or other inotify-stuff to trigger the execution of your script.
[1] http://inotify.aiken.cz/?section=incron&page=about&lang=en
Solution 3:
inotify would be the right way to do it. Tutorials are given in some LinuxForYou magazine edition for this very question.