Hm, I've recently begun using zsh primarily and this trick doesn't work there: zsh lets you know what the alias is... bash will happily find `rack` in your `$PATH` and then run it.
(Presumably because in zsh, `which which` says it's a shell built-in, whereas in bash it finds `/usr/bin/which`, so bash doesn't seem to be caring about your aliases.)
(Presumably because in zsh, `which which` says it's a shell built-in, whereas in bash it finds `/usr/bin/which`, so bash doesn't seem to be caring about your aliases.)