How do i validate length of entire regex?

I am trying to build a regex to check an email address

/\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/

works fine, but i only want it to accept up to 256 chars.

something like

/\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*${3,254}/


but ofcourse it does not work, how do i do this?
LVL 1
tim_carterAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

käµfm³d 👽Commented:
Try:

/^(?=.{3,256}$)\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/

Open in new window

0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
Ray PaseurCommented:
You might find this function useful.
<?php // RAY_email_validation.php
error_reporting(E_ALL);


// A FUNCTION TO TEST FOR A VALID EMAIL ADDRESS, RETURN TRUE OR FALSE
// SEE MAN PAGE: http://php.net/manual/en/intro.filter.php
function check_valid_email($email)
{
    // FROM THE POST AT EE, CONSIDER ONLY 256 CHARACTERS
    $email = substr(trim($email),0,256);
    
    // LIST OF BLOCKED DOMAINS
    $bogus = array
    ( '@unknown.com'
    , '@example.com'
    , '@gooseball.org'
    )
    ;

    // IF PHP 5.2 OR ABOVE, WE CAN USE THE FILTER
    if (strnatcmp(phpversion(),'5.2') >= 0)
    {
        if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE) return FALSE;
    }

    // IF LOWER-LEVEL PHP, WE CAN CONSTRUCT A REGULAR EXPRESSION
    else
    {
        $regex
        = '/'                        // START REGEX DELIMITER
        . '^'                        // START STRING
        . '[A-Z0-9_-]'               // AN EMAIL - SOME CHARACTER(S)
        . '[A-Z0-9._-]*'             // AN EMAIL - SOME CHARACTER(S) PERMITS DOT
        . '@'                        // A SINGLE AT-SIGN
        . '([A-Z0-9][A-Z0-9-]*\.)+'  // A DOMAIN NAME PERMITS DOT, ENDS DOT
        . '[A-Z\.]'                  // A TOP-LEVEL DOMAIN PERMITS DOT
        . '{2,6}'                    // TLD LENGTH >= 2 AND =< 6
        . '$'                        // ENDOF STRING
        . '/'                        // ENDOF REGEX DELIMITER
        . 'i'                        // CASE INSENSITIVE
        ;
        // TEST THE STRING FORMAT
        if (!preg_match($regex, $email)) return FALSE;
    }

    // TEST TO SEE IF THE DOMAIN IS IN OUR BLOCKED LIST
    foreach ($bogus as $badguy)
    {
        if (stripos($email, $badguy)) return FALSE;
    }

    // FILTER_VAR OR PREG_MATCH DOES NOT TEST IF THE DOMAIN IS ROUTABLE
    $domain = explode('@', $email);

    // MAN PAGE: http://php.net/manual/en/function.checkdnsrr.php
    if ( checkdnsrr($domain[1], "MX") || checkdnsrr($domain[1], "A") ) return TRUE;

    // EMAIL IS NOT ROUTABLE
    return FALSE;
}



// DEMONSTRATE THE FUNCTION IN ACTION
$e = NULL;
if (!empty($_GET["e"]))
{
    $e = $_GET["e"];
    if (check_valid_email($e))
    {
        echo "<br/>VALID: $e \n";
    }
    else
    {
        echo "<br/>BOGUS: $e \n";
    }
}


// END OF PROCESSING - CREATE THE FORM USING HEREDOC NOTATION
$form = <<<ENDFORM
<form>
TEST A STRING FOR A VALID EMAIL ADDRESS:
<input name="e" value="$e" />
<input type="submit" />
</form>
ENDFORM;

echo $form;

Open in new window

0
Pierre FrançoisSenior consultantCommented:
If you accept to code two different regexes, you can first perform a test on the length with
/.{257}/

Open in new window

and then perform a text on the structure with your initial working regex
/\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/

Open in new window


If the first expression matches, the address is too large.
0
Ultimate Tool Kit for Technology Solution Provider

Broken down into practical pointers and step-by-step instructions, the IT Service Excellence Tool Kit delivers expert advice for technology solution providers. Get your free copy now.

ozoCommented:
fred&barney@stonehenge.com
is a valid email address
0
tim_carterAuthor Commented:
/^(?=.{3,254}$)\w+([-+&.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/

This regex is perfect
0
tim_carterAuthor Commented:
Thanks.

/^(?=.{3,254}$)\w+([-+&.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/

Modified with & because that is legal in local part
0
Ray PaseurCommented:
This regex is perfect
I am always amused when I see something like that in writing!  The internet is littered with regular expressions that do not quite work right.  Many of the worst offenders are regular expressions designed to tell if an email address is valid.  That is probably the most important reason for development of this function:
http://php.net/manual/en/function.filter-var.php

Filter_var() has been available since the years-ago release of PHP 5.2.  See:
http://php.net/manual/en/filter.filters.validate.php

PHP 5.2 is now obsolete and is not supported any more. PHP 5.2 is so old it is not even given security releases.  So this is a good time to reconsider whether writing your own regex to validate emails still makes sense.  It's kind of like adjusting a carburetor.  It doesn't really matter how good you are with a carburetor.  Carburetor adjustment is an obsolete skill.  We don't have to do that any more because we have fuel injected engines.  And we don't have to tinker with email validation because we have filter_var().

Filter_var() does not check whether the email is routable.  I choose to include that test in the function posted at ID: 37749502 on line 56.  If you're sending email to yourself at localhost, you might or might not want to include that functionality.
0
tim_carterAuthor Commented:
Hi Ray,

I actually use filter_var in php to check email addresses.

Im am just practicing on regex. I do not main that it is perfect to validate an email, because there is still emails it will not validate.
0
Ray PaseurCommented:
Filter_var() is the right tool.  

You might enjoy this article if you're learning about regular expressions.
http://www.experts-exchange.com/Web_Development/Web_Languages-Standards/PHP/A_7830-A-Quick-Tour-of-Test-Driven-Development.html
0
tim_carterAuthor Commented:
Thanks ray, I will look at that article
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Regular Expressions

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.