Finding something after a search term

How can you determine if there are more bytes to a file after a certain string? I want to parse a file, find a certain combination of values, and then see if that's the end of the file or not. What will happen next depends on whether that's the end or not. Any ideas?

Is some autistic entity trying to build a spambot to poast here using the collective intelligence of /proggles/? This is a second thread about text processing that displays a lack of basic understanding.