Updated shell script to change $* to $@ and fix quoting errors

The existing lesson ignores quoting and uses $* instead of $@. This causes all example scripts to fail if a file path ever has whitespace in it.

I realize that it adds a bit of complexity to the lesson, but I think that it is worth discussing in light of the likelihood that novices will run into this issue early on.
In case we use `"$1"` instead of `$1`, what about "We also should put `$@` inside double-quotes to handle the case of parameters containing spaces (`"$@"` is equivalent to `"$1" "$2" ...`).