[oefrha]

> by unix-style long options do you mean single-dash long options (e.g. `-long` being a single option)

Yes.

> and therefore flags not allowing concatenating short options (e.g. `-r -x` can't be written `-rx`)?

Depending on the implementation concatenation of short options may be allowed; it certainly could be ambiguous. I'm not sure about flags (the golang package) though.