Regex for email field validation

[Pikachu2000]

I admit it, I've never used a ereg that wasn't cut and paste 🙂 (But I'm willing to learn!)
I'd like to know the best way to validate an email field in such a way that, for example, both:

"[e-mail]" and "[e-mail]" would be valid, while still checking the length of the TLD extension.

Can I do this with one ereg, or do I need an two and an OR operator?
A quick point in the right direction would be appreciated.

[HalfaBee]

I think ^{[A-Z0-9._%+-]+@[A-Z0-9-.]+.[A-Z]{2,4}$}

is nearly correct.

[Pikachu2000]

HalfaBee;10887682 wrote:

I think ^{[A-Z0-9._%+-]+@[A-Z0-9-.]+.[A-Z]{2,4}$}

is nearly correct.

Thanks for the response.

From what I can tell, it looks like that will check the string before the @ sign, then check from there to the last period, then check the string after the last period. Am I interpreting that right? As you can probably tell, my experience with regexes is nil, but I'm sure I'll get through it with some help from the manual and some advice from here.

[NogDog]

If using PHP PHP 5.2.0 or later:

if(filter_var($_POST['email_address'], FILTER_VALIDATE_EMAIL) == false OR
          filter_var($_POST['email_address'], FILTER_SANITIZE_EMAIL !== $_POST['email_address']))
{
   // invalid email
}

Else, from http://www.iamcal.com/publish/articles/php/parsing_email/:

function is_valid_email_address($email)
{
   $qtext = '[^\\x0d\\x22\\x5c\\x80-\\xff]';
   $dtext = '[^\\x0d\\x5b-\\x5d\\x80-\\xff]';
   $atom = '[^\\x00-\\x20\\x22\\x28\\x29\\x2c\\x2e\\x3a-\\x3c'.
   '\\x3e\\x40\\x5b-\\x5d\\x7f-\\xff]+';
   $quoted_pair = '\\x5c[\\x00-\\x7f]';
   $domain_literal = "\\x5b($dtext|$quoted_pair)*\\x5d";
   $quoted_string = "\\x22($qtext|$quoted_pair)*\\x22";
   $domain_ref = $atom;
   $sub_domain = "($domain_ref|$domain_literal)";
   $word = "($atom|$quoted_string)";
   $domain = "$sub_domain(\\x2e$sub_domain)*";
   $local_part = "$word(\\x2e$word)*";
   $addr_spec = "$local_part\\x40$domain";
   return preg_match("!^$addr_spec$!", $email);
}

[Pikachu2000]

Thank you for those examples also, NogDog. Those functions will surely come in handy. I'm also trying to wrap my mind around regex syntax in case I need it in the future. Do you know of a tutorial or article that gives a good walkthrough?

[NogDog]

I can't point you to any tutorials. Mainly I depend on the manual:
PCRE syntax details
PCRE modifiers

[Pikachu2000]

NogDog;10887726 wrote:

I can't point you to any tutorials. Mainly I depend on the manual:
PCRE syntax details
PCRE modifiers

I certainly appreciate it. I'll have a look at those and mess with it a bit. I'll get the hang of it eventually, I'm sure. Thanks for the help.

[NogDog]

It's really sort of like it's own specialized (and very terse) programming language. You can even find entire books on the subject: http://oreilly.com/catalog/9780596528126/. But once you get the hang of it, you'll wonder how you ever survived without it.

[fris]

regexlib has some nice examples

http://regexlib.com/DisplayPatterns.aspx

[bpat1434]

I always like http://www.regular-expressions.info

[nrg_alpha]

NogDog;10887713 wrote:

If using PHP PHP 5.2.0 or later:

if(filter_var($_POST['email_address'], FILTER_VALIDATE_EMAIL) == false OR
          filter_var($_POST['email_address'], FILTER_SANITIZE_EMAIL !== $_POST['email_address']))
{
   // invalid email
}

Ever since I stumbled upon this in Nog's blog, I never resorted to anything other way for checking emails. I find it a 'relaxed' version of checking.

Too many people tend to come up with regex that is too 'tight fisted' in the context of email formats, thus losing potential messages (or otherwise patterns that just don't take all formats into account correctly). By using this version, you get a more relaxed system that allows emails that are formatted correctly, which pretty much ensures some oddball valid emails that you might otherwise have not taken into account to pass through validation (and as a bonus, you don't have to bang your head on the wall when testing such regex patterns to see why they aren't working... thus saving your drywall [and perhaps cranium depending on the wall's surface] from cracking. 🙂