I shortened a pair of MTB flat bars for a S/S road runabout. Likely you're going to be putting grips on them, so the cut doesn't have to be as hairsplitting as you'd need for, say a steerer. I measured off the requisite 2" from each end, marked the spot with a Sharpie, wrapped the bar so the bench vise wouldn't mar it, then simply cut it with a hacksaw, eyeballing it to get a fairly perpendicular cut. It's a Al bar, so the saw went through it pretty easily. Cleaned up the ends with a file, reinstalled it (used a beercan shim so it fitted snugly into a 3T quill stem), fitted levers and grips, and done. This job doesn't really require that much thinking.