Remember GNU's $POSIX_ME_HARDER? Later restated more softly / less offensively as $POSIXLY_CORRECT.
Efforts to standardize Unix go way back (e.g. /usr/group in 1984). Most people hadn't yet even remotely heard of Unix and we were already needing to smooth over fragmentation. POSIX first ratified in 1988. Unevenly-conforming implementations arrived a year or few later. But that ".1" was only the first, thinnest, most obvious slice of "we should all do this the same way." Overall we've been working to bring Unix and its descendants into alignment for 40+ years. Doesn't feel fully wrangled even now. There's a reason we still might need $POSIXLY_CORRECT.
Efforts to standardize Unix go way back (e.g. /usr/group in 1984). Most people hadn't yet even remotely heard of Unix and we were already needing to smooth over fragmentation. POSIX first ratified in 1988. Unevenly-conforming implementations arrived a year or few later. But that ".1" was only the first, thinnest, most obvious slice of "we should all do this the same way." Overall we've been working to bring Unix and its descendants into alignment for 40+ years. Doesn't feel fully wrangled even now. There's a reason we still might need $POSIXLY_CORRECT.