sh (the bourne SHell) is proprietry, bash (The Bourne Again SHell) is free. bash has a heap of additional features over sh, but because a lot of commercial systems only have sh and not bash, sh is still considered the standard. If your shell scripts are never going to come into contact with any corporate big iron, you don\'t need to worry what the differences are. For all things linux, there is only bash - sh is just a symlink to bash. (Of course, there are dozens of other shells you may wish to expore, csh, ksh, zsh, ash to name a few)
Now I don\'t know what is going on in OZ with sh - try sh --version and see what you get.