core-bundle/src/Resources/contao/library/Contao/StringUtil.php
public static function stripRootDir($path)
	{
		$rootDir = System::getContainer()->getParameter('kernel.project_dir');
		$length = \strlen($rootDir);

		if (strncmp($path, $rootDir, $length) !== 0 || \strlen($path) <= $length || ($path[$length] !== '/' && $path[$length] !== '\\'))
		{
			throw new \InvalidArgumentException(sprintf('Path "%s" is not inside the Contao root dir "%s"', $path, $rootDir));
		}

		return (string) substr($path, $length + 1);
	}
public static function stripRootDir($path)
	{
		$rootDir = System::getContainer()->getParameter('kernel.project_dir');
		$length = \strlen($rootDir);

		if (strncmp($path, $rootDir, $length) !== 0 || \strlen($path) <= $length || ($path[$length] !== '/' && $path[$length] !== '\\'))
		{
			throw new \InvalidArgumentException(sprintf('Path "%s" is not inside the Contao root dir "%s"', $path, $rootDir));
		}

		return (string) substr($path, $length + 1);
	}
Strip the Contao root dir from the given absolute path

@param string $path

@return string

@throws \InvalidArgumentException