core-bundle/src/Resources/contao/library/Contao/Environment.php
public static function get($strKey)
	{
		if (isset(static::$arrCache[$strKey]))
		{
			return static::$arrCache[$strKey];
		}

		if (\in_array($strKey, get_class_methods(__CLASS__)))
		{
			static::$arrCache[$strKey] = static::$strKey();
		}
		else
		{
			$arrChunks = preg_split('/([A-Z][a-z]*)/', $strKey, -1, PREG_SPLIT_DELIM_CAPTURE|PREG_SPLIT_NO_EMPTY);
			$strServerKey = strtoupper(implode('_', $arrChunks));
			static::$arrCache[$strKey] = $_SERVER[$strServerKey];
		}

		return static::$arrCache[$strKey];
	}
public static function get($strKey)
	{
		if (isset(static::$arrCache[$strKey]))
		{
			return static::$arrCache[$strKey];
		}

		if (\in_array($strKey, get_class_methods(__CLASS__)))
		{
			static::$arrCache[$strKey] = static::$strKey();
		}
		else
		{
			$arrChunks = preg_split('/([A-Z][a-z]*)/', $strKey, -1, PREG_SPLIT_DELIM_CAPTURE|PREG_SPLIT_NO_EMPTY);
			$strServerKey = strtoupper(implode('_', $arrChunks));
			static::$arrCache[$strKey] = $_SERVER[$strServerKey];
		}

		return static::$arrCache[$strKey];
	}
Return an environment variable

@param string $strKey The variable name

@return mixed The variable value