PHP provides two alternatives for validating the form data items which are strings but are expected to be a representation of Email ID or a URL. One way to check the form element contains email/URL is with the use of RegEx (regular expressions), and the other, more convenient approach is to use filter_var() function. Let us apply both these methods and validate email and URL submitted by a form to a PHP script.

The HTML Form used for this chapter is as follows −

<h1>Email and URL Validation</h1>
<form action="hello.php" method="POST">
   <p><label for="email">Enter your email:</label>
   <input type="text" id="email" name="email"></p>
   <p><label for="URL">Enter your website<label>
   <input type = "text" id="URL" name="url"></p>
   <input type="submit">
</form>

Validation with Regex

PHP’s built-in function library includes the preg_match() function that performs a regular expression match.

preg_match(
   string $pattern,
   string $subject,
   array &$matches = null,
   int $flags = 0,
   int $offset = 0
): int|false

This function searches subject for a match to the regular expression given in pattern. preg_match() returns 1 if the pattern matches given subject, 0 if it does not, or false on failure.

A valid email ID should satisfy the following regular expression −

"/^([a-z0-9+_-]+)(.[a-z0-9+_-]+)*@([a-z0-9-]+.)+[a-z]{2,6}$/ix"

Similarly, a valid URL should satisfy the following regular expression −

"/b(?:(?:https?|ftp)://|www.)[-a-z0-9+&@#/%?=~_|!:,.;]*[-a-z0-9+&@#/%=~_|]/i"

The following function returns “1” or “0” if the string is a valid email ID.

function checkemail($str) {
   return (!preg_match("/^([a-z0-9+_-]+)(.[a-z0-9+_-]+)*@([a-z0-9-]+.)+[a-z]{2,6}$/ix", $str)) ? FALSE : TRUE;
}

Example

Let us use the checkmail() function to check whether the email field in the above HTML is valid or not, with the help of following PHP code −

<?php         
   function checkemail($str) {
      return (!preg_match("/^([a-z0-9+_-]+)(.[a-z0-9+_-]+)*@
         ([a-z0-9-]+.)+[a-z]{2,6}$/ix", $str)) ? FALSE : TRUE;
   }
   if ($_SERVER["REQUEST_METHOD"] == "POST") {
      $email = $_POST[''email''];
      if(!checkemail($email)){
         echo "Invalid email address.";
      } else {
         echo "Valid email address.";
      }
   }
?>

The HTML form is rendered as below −

Test the PHP code by entering valid/invalid email string in the email field.

The following checkURL() function checks if a string represents a valid or invalid URL, and returns “1 or “0”.

function checkURL($str) {
   return (!preg_match("/b(?:(?:https?|ftp)://|www.)
      [-a-z0-9+&@#/%?=~_|!:,.;]*[-a-z0-9+&@#/%=~_|]/i", $str)) ? FALSE : TRUE;
}

Example

The URL field extracted from the $_POST array is given as argument to the above function.

<?php         
   function checkURL($str) {
      return (!preg_match("/b(?:(?:https?|ftp)://|www.)[-a-z0-9+&@#/%?=~_|!:,.;]
         *[-a-z0-9+&@#/%=~_|]/i", $str)) ? FALSE : TRUE;
   }
   if ($_SERVER["REQUEST_METHOD"] == "POST") {
      $url = $_POST[''url''];
      if(!checkURL($url)){
         echo "Invalid URL.";
      } else {
         echo "Valid URL.";
      }
   }
?>

You can test the above code by entering URL string in the URL field of the above form.

Using filter_var() function

The built-in filter_var() function filters a variable with a specified filter.

filter_var(mixed $value, int $filter = FILTER_DEFAULT, array|int $options = 0): mixed

Depending on the enumerated filter ID as the value of $filter parameter, the $value parameter is checked and the function returns the filtered data, or false if the filter fails.

There are various predefined filter ID constants available −

Example

The following PHP script validates the email and URL data submitted by the HTML for above −

<?php
   if ($_SERVER["REQUEST_METHOD"] == "POST") {
      $email = $_POST[''email''];
      $url = $_POST[''url''];

      if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
         echo "Invalid email format and please re-enter valid emailn"; 
      }
      else
      echo "Email entered is in valid formatn";

      if (!filter_var($url, FILTER_VALIDATE_URL)) {
         echo "Invalid URL format and please re-enter valid URLn"; 
      }
      else
      echo "URL entered is in valid formatn";
   }
?>

You can test the performance of the above script by entering valid/invalid email/URL.