Regex empty string or email

Question

I found a lot of Regex email validation in SO but I did not find any that will accept an empty string. Is this possible through Regex only? Accepting either empty string or email only? I want to have this on Regex only.

Answer 1

This regex pattern will match an empty string:

^$

And this will match (crudely) an email or an empty string:

(^$|^.*@.*..*$)