Not only that, but the thing exec'ed is a limitless supply of portability problems. And it's not just *nix vs windows (e.g. do I say "ls" or "dir") because even unices vary widely in the implementation of common commands. For example, on Red Hat Linux you can just say "ps -ax" but if you want that same set of options on Solaris, better reach for /usr/ucb/ps (or put /usr/usb in your path.)
