I have this regex: ^regex*\.0-9

You do not use code tags, so it's not clear what regex you have. Please see Markup in the Monastery, Writeup Formatting Tips and How do I post a question effectively?.

I going to guess that your regex is  /^regex*\.[0-9]/ You say that your regex matches "regex.1", which I can accept, but why would you think it would match "regex.abc", since "abc" has no relation to  [0-9] (a decimal digit)? Please see perlre and perlretut.

It seems as though the ? doesnt make the \. optional.

I don't see any  ? metacharacter. (Update: And what difference would you expect it would make if the  \. were optional?)

Update: When I first read "It must also match regex, but not regex.abc." in the OP, I thought codz67 wanted the regex also to match  'regex.abc' and was puzzled why it didn't. A more careful reading brings a better understanding. See discussion below. Oh, well...