<

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x

Validation of Email Addresses with Regular Expressions

Posted on
7,850 Points
1,050 Views
3 Endorsements
Last Modified:
Experience Level: Beginner
4:57
Terry Woods
Bridging the gap, in a way you can understand, between what you want and tech that can achieve it. Websites, web based software, email...
Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions.

Video Steps

1. Consider email address RFCs

2. Look at HTML5 form input element (with type=email) regex pattern

3. Try out the given pattern on some test data

4. Explain why we shouldn't be trying to match top level domains

5. Remind about server side validation

6. Remind about an expected level of knowledge

7. Mention EE Regular Expressions Topic Area

3
Comment
Author:Terry Woods
1 Comment
LVL 111

Expert Comment

by:Ray Paseur
In addition to regular expressions, PHP has some built-in filters that can help.
http://php.net/manual/en/function.filter-var.php
http://php.net/manual/en/filter.filters.validate.php

Here is how I validate an email address.
<?php // demo/email_validation.php
/**
 * How to use a utility function to test for a valid email address
 * 'Valid' does not mean email will be received - parked domains are valid, but inactive
 *
 * http://php.net/manual/en/intro.filter.php
 * http://php.net/manual/en/function.checkdnsrr.php
 * https://tools.ietf.org/html/rfc5321
 *
 * See also:
 * https://www.experts-exchange.com/articles/3939/Registration-and-Email-Confirmation-in-PHP.html
 */
error_reporting(E_ALL);


function check_valid_email($email, $bogus=[], $route=TRUE)
{
    $valid = TRUE;

    // IF THE EMAIL STRING IS IMPROPERLY FORMED
    if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE) $valid = FALSE;

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

    // IF THE DOMAIN HAS NO MAIL-EXCHANGE RECORD
    if ($route) {
        $domain = explode('@', $email);
        if ( !checkdnsrr($domain[1]) ) $valid = FALSE;
    }

    return $valid;
}


// INJECTED DEPENDENCY - LIST OF BAD DOMAINS
$bogus = [ '@unknown.com', '@example.com', '@gooseball.org' ];


// DEMONSTRATE THE FUNCTION IN ACTION
$e = !empty($_GET['e']) ? $_GET['e'] : NULL;
if ($e)
{
    if (check_valid_email($e, $bogus))
    {
        echo "<br/>VALID: $e" . PHP_EOL;
    }
    else
    {
        echo "<br/>BOGUS: $e" . PHP_EOL;
    }
}


// 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

Featured Post

Python 3 Fundamentals

This course will teach participants about installing and configuring Python, syntax, importing, statements, types, strings, booleans, files, lists, tuples, comprehensions, functions, and classes.

Join & Write a Comment

Suggested Videos

Title Views Activity
Introduction to Accessibility (Part 1) 24
Introduction to HTML (Part 1) 111
Introduction to jQuery (Part 1) 782
Flexible Layouts 69
World Wide Web is the information superhighway as was dubbed by former US president Al-Gore. Since then, the Internet has evolved at a lightning pave as there are many ways in which it has changed the lives of all of us. E-commerce is one aspect th…
This article shows how to save the names and URLs of open Firefox tabs in a plain text file with FoxyTab, a Featured Extension. I tested it in the latest Firefox Quantum release (61.0.1 on this article's publication date), both 32-bit and 64-bit, an…

Keep in touch with Experts Exchange

Tech news and trends delivered to your inbox every month