The only thing that is required to happen is that they all obey the rules of the POSIX shell (when called as /bin/sh). Otherwise, anything goes. https://pubs.

The only thing that is required to happen is that they all obey the rules of the POSIX shell (when called as /bin/sh). Otherwise, anything goes. https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V... All the userland utilities must have the behavior (and problems) specified here: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ https://pubs.opengroup.org/onlinepubs/9699919799/utilities/