I can't find anything to support that in the IEEE POSIX ISO spec from the Austin WG, but the GNU toolset definitely supports your assertion. I think it's import

I can't find anything to support that in the IEEE POSIX ISO spec from the Austin WG, but the GNU toolset definitely supports your assertion. I think it's important to recognize that POSIX is not SCO UNIX (UNIX(tm) is effectively a trademark and nothing more at this point) which is not GNU/Linux which is not LSB(Linux Standard Base). POSIX itself is a huge PCB of bodge-wires due to legacy compliance. On the upside for systemd haters, they can appeal to the 2004 ISO standard as init.d being the "right way". But if you read the rationale behind a bunch of utilities especially in Section B, you'll see why it's so crusty. "This ..worked in SysV so we're going to keep it". The Linux Standard Base specification isn't much better. The whole argument as to 'what is UNIX' is so contrived at this point, but anyone making the argument that GNU coreutils are about composibility are correct (see page 230 of https://www.gnu.org/software/coreutils/manual/coreutils.pdf https://www.gnu.org/software/coreutils/manual/coreutils.pdf). They assert that the Bell Labs UNIX philosophy was effectively "one tool to do one thing well, orthogonal to other tools, to facilitate composibility" (the authors even dedicate an entire proceeding section to demonstrate it) but that's without any direct references to previous specifications. Anyways, I'm with you, and apparently the GNU guys claim the Bell Labs guys were with you as well.