If you don't know what's in the POSIX spec, you should go and read it. If you do this, you will learn not only what the shell must do, but also that /usr/bin/e

If you don't know what's in the POSIX spec, you should go and read it. If you do this, you will learn not only what the shell must do, but also that /usr/bin/env might not exist at all. The env utility is required, but it isn't always in /usr/bin.