Find out subdomain using Regular Expression in PHP

Question

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

Answer 1

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 />";
?>

Answer 2

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);

Answer 3

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

Answer 4

如果要使用preg_replace（），则：

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