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Editorial Team
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Asked: 2026-05-24T15:36:08+00:00

php.net has good reference material for parse_url , preg_match and general regular expressions .

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php.net has good reference material for parse_url, preg_match and general regular expressions. I’m trying to understand this snippet I found on SO here:

I’m familiar with all of the snippet excecpt this bit:

?P<domain>

What does this part do in relation to the whole. Particularly the ‘?P’. I’m assuming the <domain> just defines a key in the associative array returned.

  function getDomain($url) 
    {
    $pieces = parse_url($url);
    $domain = isset($pieces['host']) ? $pieces['host'] : '';
    if(preg_match('/(?P<domain>[a-z0-9][a-z0-9\-]{1,63}\.[a-z\.]{2,6})$/i', $domain, $regs)) 
      {
      return $regs['domain'];
      }
    return false;
    }
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1 Answer

  1. Editorial Team

    The ?P<domain> part defines the name of that group. That means that you can then access it by name with $regs['domain'] instead of by number as $regs[0]. It’s useful in large regexes since giving names to each of the groups makes it easier to understand what’s going on.

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