- strtok: documentation ( source)
- parse_url: documentation ( source)
<?php
$url = 'https://example.com/pathurl';
$bits = parse_url($url);
$sub = strtok($bits['host'], '.');
echo $sub . PHP_EOL;
$url = 'https://subdomain.example.com/pathurl';
$bits = parse_url($url);
$sub = strtok($bits['host'], '.');
echo $sub . PHP_EOL;