Regex to detect period before @ in email address

Question

Need regex which will detect first.second@domain.tld

but not detect on ([a-z0-9A-Z])@domain.tld

valid: abc123XYZ@domain.tld

invalid: abc12.de456@domain.tld

I recognize a period is legal preceeding @ in an email address but need to detect that condition.

Is there anything else we can do for you? [What have you tried?](http://mattgemmell.com/2008/12/08/what-have-you-tried/) — Herbert, Mar 11 '13 at 22:12
you can use `\.` to match the period, or you can just detect whether `isMatch([a-z0-9A-Z]*@domain.tld)` is equal to `false` — Sam I am says Reinstate Monica, Mar 11 '13 at 22:25
@SamIam That is a bad way to solve the problem. Properly formatted emails can be more complicated than that. See sputnick's answer for a general idea. — jonvuri, Mar 11 '13 at 22:30
@jrajav op just said he needed to detect weather there was a period before the address. — Sam I am says Reinstate Monica, Mar 11 '13 at 22:32
@SamIam Right, but the issue here is that your solution will not only reject addresses with no period, but also many other valid email addresses. — jonvuri, Mar 12 '13 at 00:20

score 2 · Answer 1 · answered Mar 11 '13 at 22:06

2

Assuming that you've already validated this as a proper email address:

\..*@

Which means: A ., then a sequence of 0 or more characters, then a @

answered Mar 11 '13 at 22:06

jonvuri

there you go :) didn't scroll as much as @sputnik answer is *a bit long* – CSᵠ Mar 11 '13 at 22:16

score 1 · Answer 2 · answered Mar 12 '13 at 00:59

You don't need regular expressions for this, just compare the position of the period against the at symbol:

// assuming there's already an `@` in $email
if (($p = strpos($email, '.')) !== false && $p < strpos($email, '@')) {
    echo 'invalid';
}

If there's no @ in the email address, it will not print 'invalid' because any integer will not strictly be smaller than false.

score 0 · Answer 3 · answered Mar 11 '13 at 22:05

0

\.(?=.*@) Should do the trick.

answered Mar 11 '13 at 22:05

Daedalus

I'm curious why you'd use a lookahead here. – jonvuri Mar 11 '13 at 22:07
I used look-ahead to only capture the "." instances coming before the "@", but without actually including the "@" in my match – Daedalus Mar 11 '13 at 22:08
This regex is only being used to detect a true/false match, from what I understand, so there is no need to exclude the `@` – jonvuri Mar 11 '13 at 22:10
Maybe they highlight the problem character for the user after validation. I don't know, just how I chose to write the answer :) – Daedalus Mar 11 '13 at 22:15

3 Answers3