> change the defaults over time

however this breaks backward compatibility, as you noted. in the golden age of unix it was critical to maintain backward compatibility so that local tooling didn't magically break.

HP-UX seems to have an env var UNIX95 that affects XPG4 compliance in operation/output. Solaris always had a /usr/xpg[46] path (and /usr/ucb). GNU tools have POSIXLY_CORRECT. and so on.

I never liked using any of those because then you're on some other system, or in a break glass situation, and none of the tooling works as you expect. In the today world of a near monoculture of linux, it's fine I guess. And there's no reason today that complex commands like `ss` shouldn't be controllable via env var.

love your blog, thanks for the link.