Use pattern to validate email addresses

Question

You'd use something like;

<input type="email" name="email" pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$">

So if you wanted to only allow a domain and subdomain in theory you'd use;

<input type="email" name="email" pattern="[a-z0-9._%+-]+@[example]+\.[com]{2,}/@[subdomain]+\.[example].\[com]$">

I only want to allow email responses from example.com and subdomain.example.com OR only allow email responses ending in .co.uk which is most ideal.

Any help would be appreciated.

UPDATE

Using;

pattern="[a-zA-Z0-9-]+@sub.example.co.uk" means that the validation will work.

But using:

pattern="[a-zA-Z0-9-]+@sub.example.co.uk|+@example.co.uk" means that the validation will work but also allows domains like @gmail.com etc.

UPDATE

Here's the code for the form.

<form action="./login.php" method="post">
<input type="email" id="email" minlength="13" maxlength="29" pattern="[a-zA-Z0-9-]+@subdomain@example.co.uk|+@example.co.uk" style="text-transform: lowercase" placeholder="Enter your email address." name="email" required=""><br>
<input type="submit">
</form>

Ideally I'd be able to set a list of allowed domains and specific email addresses so only jon@example.co.uk, igor@example.co.uk and stephen@example.co.uk could submit. Can you match the beginning of the email as an array or the entire thing in the format of $allowedaddresses to save exploding the @ from the domain.

[How to validate an email address using a regular expression?](https://stackoverflow.com/q/201323/3343753) — Pedro Rodrigues, Dec 22 '18 at 00:25

score 0 · Answer 1 · answered Dec 06 '18 at 01:35

Don't try to write a regular expression to validate email addresses because it's virtually impossible. The standard governing email addresses was very loosely-defined and historically people went many wildly different ways with it.
Don't try to pack too much application logic into a regular expression.

Since you're only trying to match the domain name, which is generally the only reliably sane part of an email address, you can get away with a simply matching the end of a string with a regular expression.

$allowed_domains = [
    '.co.uk',
    'bar.co.uk'
];

$forbidden_domains = [
    'baz.bar.co.uk'    
];

// make it a bit easier to manage the lists of allowed/forbidden domains
function domain_suffix_to_regex($suffix) {
    return sprintf('/.*%s$/', preg_quote($suffix));
}
$allowed = array_map('domain_suffix_to_regex', $allowed_domains);
$forbidden = array_map('domain_suffix_to_regex', $forbidden_domains);

$emails = [
    'example@foo.bar.co.uk',
    'example@bar.co.uk',
    'example@baz.bar.co.uk'
];

foreach($emails as $email) {
    $permitted = false;
    foreach($allowed as $expr) {
        if( preg_match($expr, $email) ) {
            $permitted = true;
            echo "$email allowed by expr: $expr\n";
            break;
        }
    }
    if( $permitted ) {
        foreach($forbidden as $expr) {
           if( preg_match($expr, $email) ) {
                $permitted = false;
                echo "$email forbidden by expr: $expr\n";
                break;
           }
        }
    }
    var_dump($permitted);
}

Output:

example@foo.bar.co.uk allowed by expr: /.*\.co\.uk$/
bool(true)
example@bar.co.uk allowed by expr: /.*\.co\.uk$/
bool(true)
example@baz.bar.co.uk allowed by expr: /.*\.co\.uk$/
example@baz.bar.co.uk forbidden by expr: /.*baz\.bar\.co\.uk$/
bool(false)

Thank you. How would I go about incorporating this with the form, example added to the question. — phphelpplease, Dec 06 '18 at 01:37
Oh. Uh... don't. 1. You'll have to use javascript for the added complexity, and even then it's just a courtesy to the end-user because... 2. You still have to do the validation server-side as HTML forms provide ZERO actual capacity for enforcing any rules as to what gets sent to the server. — Sammitch, Dec 06 '18 at 01:40

Use pattern to validate email addresses

1 Answers1