You don’t have to use regular rules to be generous. Isn’t this more elegant?

$url = 'http://www.baidu.com/aa/bbb';
var_dump(parse_url($url));
//array(3) {
     ["scheme"]=> string(4) "http" 
     ["host"]=> string(13) "www.baidu.com" 
     ["path"]=> string(7) "/aa/bbb"
    }

if(strncmp('http://', $url, 7) === 0 || strncmp('https://', $url, 8)) {
  $host = substr($url, strpos($url, '/', strncmp('http://', $url, 7) ? 8 : 7));
} else {
  $host = null;
}

If possible, try not to use regular expressions

There are many methods for this. Since the requirement is regular, please see the code below

    $str= 'http://www.baidu.com/aa/bbb';
    $patten = '/(http[s]?:\/\/\w*.\w*.\w*\/).*/';
    preg_match($patten, $str, $match);

    echo $match[1];

https://www.bytelang.com/o/s/...

Refer to the answers below

Isn’t it better to use explode? Why use regular expressions