Another Flat File question.

I know I've asked this before but I don't believe I asked the question correctly. I have a flat file database that is delimited with colons. This file will have new records added to it on a regular basis. What I want to do is be able to search that file based on a keyword that is inputted by a user, then it will search that database comparing each record for that value, if that value returns true, I want it to display the results of that record. How would I do this when I don't know the number of records that will be searched (since it will rise and fall almost daily)? Also, how would I create a dynamic array? I hope this makes sense to someone, I've been pulling my hair out on this. Thanks!