Do you mean deleting everything until you find a RE in the file, or do you mean processing the file with a RE?
I think it merely depends on what exactly you want to do. Is it a big file, or just a few lines? Is it a complex RE you want to process? Be more exact please.
"We are all prompted by the same motives, all deceived by the same fallacies, all animated by hope, obstructed by danger, entangled by desire, and seduced by pleasure."
- Samuel Johnson