Question

I need to write regex(.NET) that match string:
start with a letter, can contain letters, numbers, periods, hyphens, 1 underscore and follow ‘@’. I tried the follow one, but it doesn’t match ‘a_bc12@’ for example.

How to fix it?

^[A-Za-z][A-Za-z0-9-]+_{0,1}(?=@)

EDITED:
it should contain {3,10} length.

Answer 1

You will need to allow characters after the underscore again:

/^[A-Za-z][A-Za-z0-9\.-]*_?[A-Za-z0-9\.-]*(?=@)/

Also, I’ve added the periods and made the strings before and after the underscore optional.