/bin/sh is NOT required by POSIX, they explicitly warn that it may not exist[1].
> Applications should note that the standard PATH to the shell cannot be assumed to be either /bin/sh or /usr/bin/sh, and should be determined by interrogation of the PATH returned by getconf PATH , ensuring that the returned pathname is an absolute pathname and not a shell built-in.
> Applications should note that the standard PATH to the shell cannot be assumed to be either /bin/sh or /usr/bin/sh, and should be determined by interrogation of the PATH returned by getconf PATH , ensuring that the returned pathname is an absolute pathname and not a shell built-in.
[1] https://pubs.opengroup.org/onlinepubs/9799919799/