This if fun, few suggestions.
The first command I ran was `ls`, which worked as expected, but then I tried running `./cowsay blah`, which didn't work. I wasn't sure how to run it until eventually I guessed `sh cowsay blah`, and it worked.
Maybe make the `./` shortcut for executing stuff?
While I'm not sure how much work it would be, it might also be kind of cool to implement the `cd` command as well.