> 4.11 Does rc have ... built in?
It is not by accident that rc has fewer built-in commands than
most shells other than the original Bourne shell. The
underlying philosophy, eloquently summarized by Boyd Roberts, is
that a shell is there to run other programs, not to have other
programs built into it. By having a well-defined role, rc has
remained small and simple, properties that lead to better
performance, fewer bugs, and a more thorough understanding of
the shell by its users.