Tip #220   Actively Monitor a File

This is a way to monitor "/var/log/messages" or any file for certain changes.
The example below actively monitors "stuff" for the word "now" and as soon as "now" is added to the file, the contents of msg are sent by email

$ tail -f stuff | awk ' /now/ { system("mail -s \"Now Occured\"  mail@foo.com < msg") }'