Extracting Domain Names from Subdomains in PHP

In PHP, obtaining the root domain name from a subdomain is a common task. Consider a scenario where you encounter variables like these:

here.example.com
example.com
example.org
here.example.org

You aim to transform these values into their root domain names, such as example.com or example.org. To achieve this, a well-crafted function is required.

Solution

The following snippet demonstrates a function called get_domain() that effectively extracts the root domain name:

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 utilizes the built-in parse_url() function to break down the URL and retrieve the host component. Subsequently, it employs a regular expression to validate and extract the root domain name, ensuring that it adheres to common domain naming conventions.

By calling get_domain() with the desired URL, you can effortlessly isolate the root domain name:

print get_domain("http://somedomain.co.uk"); // outputs 'somedomain.co.uk'

In cases where the URL does not conform to acceptable domain structures, the function gracefully handles these edge cases by returning false.