Try posting your complete regex from "s" through ";" (e.g. s/([ A-Z]+)/myreplacement/gixm; -- it will make it clear what you're actually applying.

Even better, post a small chunk of runnable code. It sounds from previous posts that you're just reading in lines and processing them in a pretty straightforward way, so the code should be quite short.

A couple hours with a regex tutorial would also help you get going faster- the questions you're posting are chapter 1 or 2 kind of things, because they're almost the first thing everyone wants to do.