PHP function to get the subdomain of a URL

Here's a one line solution:

array_shift((explode('.', $_SERVER['HTTP_HOST'])));

Or using your example:

array_shift((explode('.', 'en.example.com')));

EDIT: Fixed "only variables should be passed by reference" by adding double parenthesis.

EDIT 2: Starting from PHP 5.4 you can simply do:

explode('.', 'en.example.com')[0];

Uses the parse_url function.

$url = 'http://en.example.com';

$parsedUrl = parse_url($url);

$host = explode('.', $parsedUrl['host']);

$subdomain = $host[0];
echo $subdomain;

For multiple subdomains

$url = 'http://usa.en.example.com';

$parsedUrl = parse_url($url);

$host = explode('.', $parsedUrl['host']);

$subdomains = array_slice($host, 0, count($host) - 2 );
print_r($subdomains);

You can do this by first getting the domain name (e.g. sub.example.com => example.co.uk) and then use strstr to get the subdomains.

$testArray = array(
    'sub1.sub2.example.co.uk',
    'sub1.example.com',
    'example.com',
    'sub1.sub2.sub3.example.co.uk',
    'sub1.sub2.sub3.example.com',
    'sub1.sub2.example.com'
);

foreach($testArray as $k => $v)
{
    echo $k." => ".extract_subdomains($v)."\n";
}

function extract_domain($domain)
{
    if(preg_match("/(?P<domain>[a-z0-9][a-z0-9\-]{1,63}\.[a-z\.]{2,6})$/i", $domain, $matches))
    {
        return $matches['domain'];
    } else {
        return $domain;
    }
}

function extract_subdomains($domain)
{
    $subdomains = $domain;
    $domain = extract_domain($subdomains);

    $subdomains = rtrim(strstr($subdomains, $domain, true), '.');

    return $subdomains;
}

Outputs:

0 => sub1.sub2
1 => sub1
2 =>
3 => sub1.sub2.sub3
4 => sub1.sub2.sub3
5 => sub1.sub2

http://php.net/parse_url

<?php
  $url = 'http://user:[email protected]/path?argument=value#anchor';
  $array=parse_url($url);
  $array['host']=explode('.', $array['host']);

  echo $array['host'][0]; // returns 'en'
?>

As the only reliable source for domain suffixes are the domain registrars, you can't find the subdomain without their knowledge. There is a list with all domain suffixes at https://publicsuffix.org. This site also links to a PHP library: https://github.com/jeremykendall/php-domain-parser.

Please find an example below. I also added the sample for en.test.co.uk which is a domain with a multi suffix (co.uk).

<?php

require_once 'vendor/autoload.php';

$pslManager = new Pdp\PublicSuffixListManager();
$parser = new Pdp\Parser($pslManager->getList());
$host = 'http://en.example.com';
$url = $parser->parseUrl($host);

echo $url->host->subdomain;


$host = 'http://en.test.co.uk';
$url = $parser->parseUrl($host);

echo $url->host->subdomain;

PHP function to get the subdomain of a URL

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