Hi
i have this problem. I have website zetorbar.cz with two subdomains: brandys.zetorbar.cz and liberec.zetorbar.cz.
I have different layout.css files for the subdomains and main domain. What I need is put different content in RightBar directly to subdomain.
I have this code in HomePage.php:

function PostersRight($num=5) {
	
		if ($_SERVER['HTTP_HOST']=="www.zetorbar.cz" || $_SERVER['HTTP_HOST']=="www.zetorbar.cz" )
			{
			$news = DataObject::get_one("ZetorPostersHolder");
			}
		elseif ($_SERVER['HTTP_HOST']=="liberec.zetorbar.cz" || $_SERVER['HTTP_HOST']=="liberec.zetorbar.cz" )
			{
			$news = DataObject::get_one("LiberecPostersHolder");
			}
		elseif ($_SERVER['HTTP_HOST']=="brandys.zetorbar.cz" || $_SERVER['HTTP_HOST']=="brandys.zetorbar.cz" )
			{
			$news = DataObject::get_one("BrandysPostersHolder");
			}
		else
			{
			$news = DataObject::get_one("ZetorPostersHolder");
			}

		return ($news) ? DataObject::get("Plakat", "ParentID = $news->ID", "", "", "") : false;
	}

It says, that when I open:
liberec.zetorbar.cz, i get LiberecPostersHolder on the RightBar. And its OK

but when I open:
brandys.zetorbar.cz i get ZetorPostersHolder, or
www.zetorbar.cz i get BrandysPostersHolder

In the CMS I have three HomePages. One for www.zetorbar.cz and zetorbar.cz, second for brandys.zetorbar.cz and third for liberec.zetorbar.cz

I use SS 2.4.5

Are you using the subsites module? http://silverstripe.org/subsites-module/

It actually provides methods for detecting which sub-site you're on