Find out subdomain using Regular Expression in PHP

Hi guys,

Sorry if this is too little of a challenge to be suited as a stack overflow question, but I'm kind of new to Regular Expressions.

My question is, what is the regular expression that returns the string "token" for all the examples bellow?

• token.domain.com
• token.domain.com/
• token.domain.com/index.php
• token.domain.com/folder/index.php
• token.domain.com/folder/subfolder
• token.domain.com/folder/subfolder/index.php
• (added after edit)
• domain.com
• domain.com/

Im trying to use inside an preg_replace function in order to find out the subdomain of the current page from the $_SERVER['SERVER_NAME'] variable.

Thank you in advance, titel

Edit note: Sorry chaos and sebnow , I edited my question, what I initially meant, but forgot to write, was that this would work without any subdomain at all - case in which it would return an empty sting or NULL

From stackoverflow

• If you want to use preg_replace(), then:

  preg_replace('/\..*/', '', $_SERVER['SERVER_NAME'])
  

• The following regex would capture any string before a full stop (the subdomain) and the rest of the domain:

  ^([^.]+)\..*$
  

  I don't see the need for regex to do this though. It would be much easier to split by the full stop and get the first element:

  list($subdomain, $rest) = explode('.', $_SERVER['SERVER_NAME'], 2);
  

• preg_replace('/^(?:([^\.]+)\.)?domain\.com$/', '\1', $_SERVER['SERVER_NAME'])
  

  Edit: What does the following output for you:

  <?php
      echo preg_replace('/^(?:([^\.]+)\.)?domain\.com$/', '\1', "sean.domain.com") . "<br />";
      echo preg_replace('/^(?:([^\.]+)\.)?domain\.com$/', '\1', "titel.domain.com") . "<br />";
      echo preg_replace('/^(?:([^\.]+)\.)?domain\.com$/', '\1', "domain.com") . "<br />";
  ?>
  

  titel : :( unfortunately the solution you described does not seem to work in my case

  titel : It does work now, I guess I misspelled something while I was passing the script to use my actual domain. Anyways, thanks a lot. Constantin TOVISI

• preg_match('@^([a-zA-Z0-9]*.)?([a-zA-Z0-9]+).([a-zA-Z]{2,4})$@',$_SERVER["HTTP_HOST"], $matches);