Question

Regex Expression for finding a string which has one @ and should not start with . or end with . Meaning hello@Same is valid .hello@Same, hello@Same. and hello@sdj@same are all invalid

What is the problem in (^([^@]+)@([^@])+$)(^[^\\.].*$)(^.*[^\\.]$).

All these three parts work individually but when we put together doesn’t work

Answer 1

You can’t just concatenate regular expressions if you want to match
all of them.

Another thing that is wrong is trying to validate email addresses
with a regular expression. This just does not work well. The only
way to find out if the user entered a valid adress is to send an
email.

A regular expression that matches your specifications would be

^(?=[^@]+@[^@]+$)[^.].*[^.]$

but, as I said, thats not a great way to validate email adresses. Check this link for horrible counter examples. =)