Further, grep (and any of its similar siblings) works just fine for such a task, is deterministic, won't feed you bullshit, and doesn't charge you tokens to do

Further, grep (and any of its similar siblings) works just fine for such a task, is deterministic, won't feed you bullshit, and doesn't charge you tokens to do a worse job than existing free tools will do well. Better yet, from my experience with the dithering pace of LLMs, you'll get your answer quicker, too.