Just check the spec itself. It pretty much describes the expected commandline syntax and behavior for commands the coreutils provide[0]. GNU coreutils is on it

Just check the spec itself. It pretty much describes the expected commandline syntax and behavior for commands the coreutils provide[0]. GNU coreutils is on its own a superset of a part of the POSIX spec (they started as rewrites of several Unix utilities), which mostly means that they added a bunch of extra flags and options. The other half of this is GNU bash which includes the non-command parts of POSIX such as shell syntax. POSIX itself meanwhile is basically a reverse spec (very much like how the C standard isn't really a standard, it's just a collective set of rules all notable C compilers follow); it was made to unify all the various Unix offshoots that were being developed and define a common set of commandline utilities and rules that they all shared. (Nowadays, that's mostly the BSDs, Linux and MacOS. Windows is the only notable OS that doesn't really do anything with POSIX besides a few aliases.) [0]: See for example the POSIX reference for cp and you'll see it's pretty similar to the GNU cp manpage - https://pubs.opengroup.org/onlinepubs/9699919799/utilities/cp.html https://pubs.opengroup.org/onlinepubs/9699919799/utilities/c...