Thank you all for your responses, the Monastery has not failed me yet!

BrowserUk, your response provided me with the answer. I realized that my issue was not with grep, but rather with split. I did not realize that split using null (split //) would split by character (e.g. "32" would become 3, 2).

Now I see when the summing takes place. The book glossed over this, but it would have been nice if it had just noted that to jog my memory, which is not so great anymore.