I can&#x27;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&#x27;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&#x2F;Linux which is not LSB(Linux Standard Base).<p>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 &quot;right way&quot;. But if you read the rationale behind a bunch of utilities especially in Section B, you&#x27;ll see why it&#x27;s so crusty. &quot;This ..worked in SysV so we&#x27;re going to keep it&quot;. The Linux Standard Base specification isn&#x27;t much better.<p>The whole argument as to &#x27;what is UNIX&#x27; is so contrived at this point, but anyone making the argument that GNU coreutils are about composibility are correct (see page 230 of <a href="https:&#x2F;&#x2F;www.gnu.org&#x2F;software&#x2F;coreutils&#x2F;manual&#x2F;coreutils.pdf" rel="nofollow">https:&#x2F;&#x2F;www.gnu.org&#x2F;software&#x2F;coreutils&#x2F;manual&#x2F;coreutils.pdf</a>). They assert that the Bell Labs UNIX philosophy was effectively &quot;one tool to do one thing well, orthogonal to other tools, to facilitate composibility&quot; (the authors even dedicate an entire proceeding section to demonstrate it) but that&#x27;s without any direct references to previous specifications.<p>Anyways, I&#x27;m with you, and apparently the GNU guys claim the Bell Labs guys were with you as well.