Regex in PHP not working - php

Question

My regex is:
$regex = '/(?<=Α: )(([\w-\.]+)#((?:[\w]+\.)+)([a-zA-Z]{2,4}))/';
My content among others is:
Q: Email Address
A: name#example.com
Rad Software Regular Expression Designer says that it should work.
Various online sites return the correct results.
If I remove the (?<=Α: ) lookbehind the regex returns all emails correctly.
When I run it from php it returns no matches.
What's going on?
I've also used the specific type of regex (ie (?<=Email: ) with different content. It works just fine in that case.

Answer 1

You are not most likely not using DOTALL flag s here which will make DOT match newlines as well in your regex:
$str = <<< EOF
Q: Email Address
A: name#example.com
EOF;
if (preg_match_all('/(?<=A: )(([\w-\.]+)#((?:[\w]+\.)+)([a-zA-Z]{2,4}))/s',
$str, $arr))
print_r($arr);
OUTPUT:
Array
(
[0] => Array
(
[0] => name#example.com
)
[1] => Array
(
[0] => name#example.com
)
[2] => Array
(
[0] => name
)
[3] => Array
(
[0] => example.
)
[4] => Array
(
[0] => com
)
)

Answer 2

This is my newer monster script for verifying whether an e-mail "validates" or not. You can feed it strange things and break it, but in production this handles 99.99999999% of the problems I've encountered. A lot more false positives really from typos.
<?php
$pattern = '!^[^#\s]+#[^.#\s]+\.[^#\s]+$!';
$examples = array(
'email#email.com',
'my.email#email.com',
'e.mail.more#email.co.uk',
'bad.email#..email.com',
'bad.email#google',
'#google.com',
'my#email#my.com',
'my email#my.com',
);
foreach($examples as $test_mail){
if(preg_match($pattern,$test_mail)){
echo ("$test_mail - passes\n");
} else {
echo ("$test_mail - fails\n");
}
}
?>
Output
email#email.com - passes
my.email#email.com - passes
e.mail.more#email.co.uk - passes
bad.email#..email.com - fails
bad.email#google - fails
#google.com - fails
my#email#my.com - fails
my email#my.com - fails
Unless there's a reason for the look-behind, you can match all of the emails in the string with preg_match_all(). Since you're working with a string, you would slightly modify the regex slightly:
$string_only_pattern = '!\s([^#\s]+#[^.#\s]+\.[^#\s]+)\s!s';
$mystring = '
email#email.com - passes
my.email#email.com - passes
e.mail.more#email.co.uk - passes
bad.email#..email.com - fails
bad.email#google - fails
#google.com - fails
my#email#my.com - fails
my email#my.com - fails
';
preg_match_all($string_only_pattern,$mystring,$matches);
print_r ($matches[1]);
Output from string only
Array
(
[0] => email#email.com
[1] => my.email#email.com
[2] => e.mail.more#email.co.uk
[3] => email#my.com
)

Answer 3

The problem is that your regular expression contains Α, which has an accent over it, but the content contains A, which doesn't. So the lookbehind doesn't match.
I change the regex to:
$regex = '/(?<=A: )(([\w-\.]+)#((?:[\w]+\.)+)([a-zA-Z]{2,4}))/';
and it works.

Answer 4

Outside of your regex issue itself, you should really consider not trying to write your own e-mail address regex parser. See stackoverflow post: Using a regular expression to validate an email address on why -- upshot: the RFC is long and demanding on your regex abilities.

Answer 5

The A char in your subject is the "normal" char with the code 65 (unicode or ascii). But The A you use in the lookbehind of your pattern have the code 913 (unicode). They look similar but are different.