Validating email input in form using PHP

I'm creating a form in PHP that contains a field called email where the user needs to enter his/her email ID. In order to ensure that the mail ID entered is authentic in terms of sy开发者_开发知识库ntax (eg. username_123@domain.com is valid) I need to append some kind of validation to it. I find the situation quite nebulous as I don't understand how to check if the mail ID entered contains an @ symbol etc. Kindly help. Thanks. :)

Best solution is to just do:

if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
   ...
}

and let PHP handle the heavy work for you. Otherwise, if you want to be strictly correct and use a regex directly yourself, you'll be stuck with this monstrosity:

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])

for strict RFC2822 compliance.

First you need to define valid e-mail.

There are different approaches to this depending on how important is this validation to you.

Some folks use crazy by-the-RFC regexps.

Another extreme is save anything user entered and later try sending confirmation e-mail to that address. No confirmation = bad e-mail.

You'll probably want something in between: make sure there's an @ in the middle, for example:

$email_arr = explode('@', $email);
if (sizeof($email_arr) !== 2 || $email_arr[0] == '' || $email_arr[1] == '')
    ... // definitely not valid

UPD: Marc B nailed it with filter_var($email, FILTER_VALIDATE_EMAIL) That's probably the best way.

You can use regex to validate the format:

<?php  

$email = "someone@example.com";  // or perhaps $_POST['email'];

if(eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$", $email)) {   

    echo "Valid email address."; 
} 
else {   
    echo "Invalid email address."; 
}  

?> 

http://php.net/manual/en/function.eregi.php

From my own code:

if( !preg_match( "(^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$)i", $email))
    echo "E-mail address invalid";

A very small number of legitimate addresses may fail, such as anything @example.info, and any email address that uses unusual characters, but for the most part this works nicely.