get exect domain name in a string

Hi all
If I have many urls,
mail.google.com.pk
mail.google.com
google.com
google.com.pk

how I get only google in output, please suggest me idea

 

@sarahk @PoPSiCLe please help

 

This is sorta ambiguous - do you need this to recognize any TLD, and only the domain itself? Note: a "domain" in this setting is not just the name "Google" - it's actually "Google.com"
However, this code does what you want on the example above:

<?php
$domain_array = array('mail.google.com.pk','mail.google.com','google.com','google.com.pk');
foreach($domain_array as $key => $value) {
   $tld_array = array('com','com.pk','net','org','me','co.uk','no','se');
   $url_ex = array_reverse(explode('.',$value));
   if (!in_array($url_ex[0],$tld_array)) {
     if (!in_array($url_ex[1].'.'.$url_ex[0],$tld_array)) {
       echo 'Couldn\'t find TLD';
     } else {
       echo $url_ex[2].PHP_EOL;
     }
   } else {
     echo $url_ex[1].PHP_EOL;
   }
}
?>

PHP:

However, you will need to update the $tld_array to match more TLDs, if needed.