Parsing Domain Names from Subdomains in PHP

In PHP, extracting the root domain name from a subdomain is a common task. This is useful when you need to identify the main website associated with a subdomain. To accomplish this, let's explore a solution.

The provided code snippet leverages the parse_url function to break down the URL into its components, including the domain name. Subsequently, it employs a regular expression to isolate the root domain, disregarding the subdomain.

The following example illustrates the usage of this function:

print get_domain("http://here.example.com"); // outputs 'example.com'

function get_domain($url)
{
  $pieces = parse_url($url);
  $domain = isset($pieces['host']) ? $pieces['host'] : '';
  if (preg_match('/(?P[a-z0-9][a-z0-9\-]{1,63}\.[a-z\.]{2,6})$/i', $domain, $regs)) {
    return $regs['domain'];
  }
  return false;
}

This function effectively extracts the root domain name from any URL, whether it contains a subdomain or not. By applying this technique, you can reliably identify the primary domain associated with any subdomain.