> Second, in principle, there's nothing to enforce that a UNIX shell must have echo as a built-in, and therefore, it's important to have the external utility /

> Second, in principle, there's nothing to enforce that a UNIX shell must have echo as a built-in, and therefore, it's important to have the external utility /bin/echo as a fallback. I read here https://en.wikipedia.org/wiki/POSIX#Overview https://en.wikipedia.org/wiki/POSIX#Overview that echo has been standardized for POSIX, can you elaborate further ?