As SwingNinja said an oscillating tool is good, but if the wood is oak it may struggle to make the cut. It'll cut through pine easily enough, but for hard wood a circular saw will cut straighter. Although you'll want to stop short of the end of the cabinet and finish the cut with a hand saw or skill/saber saw. If your in a tight location because of the counter, you may want a compact circular saw like a Rockwell Versacut.