This function checks if the provided URL is of external site or not. Returns boolean.

is_external.php

<?php // do not copy this line.


/**
 * Is External
 * 
 * This function checks if the provided URL is external or not. 
 * 
 * Author URL: https://zeshanahmed.com/
 * 
 * @param string $url URL to be checked
 * @author Zeshan Ahmed
 * @return boolean
 */
function is_external( $url ) {
  $url_parts = parse_url( $url );
  return ! empty( $url_parts['host']) && strcasecmp( $url_parts['host'], $_SERVER['HTTP_HOST'] );
}