How to get only the domain of a URL?

PHP already has a function that separates all the elements of a URL.

It's just the parse_url :

$url = 'http://exemplo.com/pasta/pasta2/past/ficheiro.php';
$elementos = parse_url($url);

echo $elementos['host']; // 'exemplo.com'

If you want a specific part, use the second parameter:

echo parse_url($url, PHP_URL_HOST);  // 'exemplo.com'

See working at IDEONE .

These are the options for the second parameter:

 PHP_URL_SCHEME     // retorna string  - ex: http
 PHP_URL_HOST       // retorna string  - ex: site.com
 PHP_URL_PORT       // retorna inteiro - ex: 443
 PHP_URL_USER       // retorna string  - ex: admin
 PHP_URL_PASS       // retorna string  - ex: swordfish
 PHP_URL_PATH       // retorna string  - ex: /blog
 PHP_URL_QUERY      // retorna string  - ex: secao=esportes
 PHP_URL_FRAGMENT   // retorna string  - ex: ancora2

If you want to use more than one part, better get the entire array:

$partes = parse_url($url); // retorna array associativo

and use all the parts that matter:

echo $partes['scheme'].'://'.$partes['host'].$partes['path'];

More details in the manual:

  

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