I want a pop up notification when a file has certain info written to it
I don't think a network filesystem is going to give you enough state information to do this quite as simply as you asked.  One solution would be this:

On the server side, run a script that looks for your 'successful' string as you described.  When it finds the string, have it write a new file into the shared directory.

On the remote side, run a script that checks for this new file, e.g.:

test -f newfilename &amp;&amp; echo 'Success!' &amp;&amp; rm newfilename


Once you've been notified, you can delete this new file and loop around for the next time.  The file creation and deletes should be reliably communicated across the network.