In most societies today, keeping one's nails trimmed within a few mms of the top of the nail plate is the grooming standard. Do we have evidence that clipping nails when they reached a certain length was a regular grooming ritual in ancient societies? By "ancient societies", I'm referring to the societies that popularly come to mind: Ancient Rome, Greece, Egypt, and the successive Mesopotamian empires of the Biblical Old Testament. Would nail clipping have been performed with some type of crude file or a knife perhaps?
Yes; in Ancient Greece and Rome at least, there were barbers who provided a range of services that were huge compared to their modern equivalent: trimming beards, cutting hair, and yes, trimming nails:
The third part of the barber's work was to pare the nails of the hands, an operation which the Greeks expressed by the words ὀνυχίζειν and ἀπονυχίζειν (Aristoph. Eq. 706; and Schol.; Theophrast. Charact. c26; Pollux, VII.165). The instruments used for this purpose were called ὀνυχιστήρια, sc. μαχαίρια (Pollux, X.140).
The practice is so old that it goes beyond history and into archaeology; here are some nail grooming tools from the Hallstatt culture:
I'm sure you can find older ones if you try.
This should all be obvious because, unless you do a lot of manual work, nails grow and keep growing. If you don't trim them they may split and break in ways that injure your finger too. So it should be as old as other forms of grooming, like hair cutting.
Even if you don't have tools to do so, you can file them against a rough surface, or bite them, which is apparently what gorillas also do.