That is another can of worms. For now, I'm worried only about the shell interpreter and builtins.

`echo` in most shells is not `/bin/echo`, it's actually an internal implementation (external echo means forking at every output, which is super slow).

The portability of other cor utils is also a clown fiesta, and most likely the best solution for now is "use gnu", which sometimes feels like "best viewed in internet explorer"-era shinenigans.