The only valid regex is (.+). Maybe add a separate country field (especially because some Americans wholeheartedly believe that the entire world should understand that “foobar, TX” means “foobar, Texas, United States”) (don’t get me started on states whose abbreviations are also ISO country codes).

Unfortunately I guess business people only care about getting fewer support calls for missing shipping details, not correctness or a couple of calls from customers who live in the boonies. Then the proper answer is a form with a bunch of fields… which Americans will inevitably fuck up by making the “State” field mandatory despite most countries not having an equivalent.

What I’d really do is use one of those services that automatically fill on the address using google maps or whatever. Not perfect, probably not free, but a whole lot less work for presumably way fewer PEBCAKs from customers.