A 25k long search string? Is your text so similar that you need to search 25000 characters to be sure of a match. Assuming the regex engine can even deal with that, the search efficiency is going to be pretty poor.

Or do you mean 25000 different strings? That has problems as well.

I think, rather than you tell us how you think it should be done, give us the problem you are trying to solve - in detail. This whole thing sounds wrong from the start, as I read it.

There are a lot of other tools out there like comm for example.