Why does this regex for emails not work

Question

I'm trying to make a regex to match email addresses, like any of these:

[email protected]
[email protected]
[email protected]

I've written this regex:

$pattern = "/[\-\.\_a-z0-9]+(\@){1}[\-\.\_a-zA-Z0-9]+(\.){1}[\-a-z0-9]+/i";

and here is some code that I am using to test it:

$str = "[email protected] was the email address associated with another one, [email protected]";
$pattern = "/[\-\.\_a-z0-9]+(\@){1}[\-\.\_a-zA-Z0-9]+(\.){1}[\-a-z0-9]+/i";
preg_match_all($pattern, $str, $matches);
var_dump($matches);

(The text between the emails is filler) It's supposed to do as follows:

Check for a username that can include one or more periods, dashes, underscores, or alphanumeric characters.
Check for one and only one (required) "@" sign.
Check for a domain or any number of subdomains (alphanumeric + periods + dashes)
Check for a period followed by alphanumeric or dash characters.

When I test the code above, I get this output:

array(3) {
    [0] => array(2) {
        [0] => string(22) "[email protected] was"
        [1] => string(22) "[email protected]"
    }
    [1] => array(2) {
        [0] => string(1) "@"
        [1] => string(1) "@"
    }
    [2] => array(2) {
        [0] => string(1) " "
        [1] => string(1) "r"
    }
 }

Why is it matching so many other characters, such as single @ signs and the letter "r"? Why does the very first email contain the word was? I never tested for spaces to my knowledge...

There's lots of email addresses that aren't anything like those. — Ignacio Vazquez-Abrams, Aug 16 '12 at 07:09
`filter_var($email, FILTER_VALIDATE_EMAIL)` to the rescue :) — Ja͢ck, Aug 16 '12 at 07:10
First off Preg_match will match based on groups such as: `(\@)` — Sammaye, Aug 16 '12 at 07:10
The other results that are returned (matches[1] and matches[2]) are the backreferences returned due to use of parenthesis. The result in matches[0] is the list of complete regex matches. — Karan Punamiya, Aug 16 '12 at 07:11
Infact your pasted results are odd because this is what I get: `Array ( [0] => [email protected] [1] => @ [2] => . )` — Sammaye, Aug 16 '12 at 07:15
I get extraneous results vbecause of the groups you are using. If you took out the groups my preg_match will find only the email. — Sammaye, Aug 16 '12 at 07:17
@KaranPunamiya Is there are difference between `(\@)` and `[\@]`? It doesn't matter to me. I know that one is a group and the other a char class, but when using one char does it matter? — apparatix, Aug 16 '12 at 07:18
So I use: `/[\-\.\_a-z0-9]+[\@]{1}[\-\.\_a-zA-Z0-9]+[\.]{1}[\-a-z0-9]+/` and it returns: `Array ( [0] => [email protected] )` — Sammaye, Aug 16 '12 at 07:18

score 1 · Accepted Answer · answered Aug 16 '12 at 07:35

To answer the question from the comments. The problem was using groups within regex which means that preg_match_all was matching on those groups separately as well.

Changing the regex to:

/[\-\.\_a-z0-9]+[\@]{1}[\-\.\_a-zA-Z0-9]+[\.]{1}[\-a-z0-9]+/

Returned:

Array
(
    [0] => Array
        (
            [0] => [email protected]
            [1] => [email protected]
        )

)

Using the OPs test text.

score 0 · Answer 2 · answered Aug 16 '12 at 07:16

0

PHP has built in filters to check for things like e-mail validity now. More specifically, you might want to look into filter_var() and the FILTER_VALIDATE_EMAIL filter.

Sample usage:

$valid_email = filter_var($email, FILTER_VALIDATE_EMAIL);
if($valid_email)
        echo "Hooray!";

All three of your sample e-mail addresses should return the "hooray!"

answered Aug 16 '12 at 07:16

noko

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Note: If you are looking for complete domains only within emails then validate_email will also validate incomplete domains such as `example@example`. Even though this is a valid email is might be undesired behaviour within most web apps. – Sammaye Aug 16 '12 at 07:25

score 0 · Answer 3 · edited May 23 '17 at 12:12

0

Validating email addresses (with regexp and otherwise) is problematic; see here: Using a regular expression to validate an email address.

edited May 23 '17 at 12:12

Community

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1

answered Aug 16 '12 at 08:37

mkataja

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Why does this regex for emails not work

3 Answers3