PHP detect if in subdirectory

if ($handle = opendir('directory/subdirectory/')) {

    while (false !== ($entry = readdir($handle))) {

        if (strpos($entry, '.php') !== false) {
          echo $entry."<br>";
        }
    }

    closedir($handle);
}

My answer is not 100% complete because it hasn't been tested on all server environments, but I can confirm this will work if using the embedded PHP web engin or using an apache server with a symlinked web folder. The function returns the subfolder in the form /folder because that is what I needed. If someone can check Nginx it will help a lot. Notice the use of CONTEXT_DOCUMENT_ROOT vs DOCUMENT_ROOT && SCRIPT_NAME vs REQUEST_URI because that could mean a router URL vs actual live file. To use as per the asked question you could say

If (!empty(getSubFolder())) {
  //Do some stuff here
}

/**
     * Logic to determine the subfolder - result must be /folder
     */
    function getSubFolder() {

        //Evaluate DOCUMENT_ROOT && CONTEXT_DOCUMENT_ROOT
        $documentRoot = "";
        if (isset($_SERVER["CONTEXT_DOCUMENT_ROOT"])) {
            $documentRoot = $_SERVER["CONTEXT_DOCUMENT_ROOT"];
        } else
            if (isset($_SERVER["DOCUMENT_ROOT"])) {
                $documentRoot = $_SERVER["DOCUMENT_ROOT"];
            }
            $scriptName = $_SERVER["SCRIPT_FILENAME"];



            //echo str_replace($documentRoot, "", $scriptName);
            $subFolder = dirname( str_replace($documentRoot, "", $scriptName));

            if ($subFolder === "/" || (str_replace($documentRoot, "", $scriptName) === $_SERVER["SCRIPT_NAME"] && $_SERVER["SCRIPT_NAME"] === $_SERVER["REQUEST_URI"])) {
                $subFolder = null;
            }

            return $subFolder;
    }