Count number of lines by suffix of files

LineCounter.php

<?php
/**
 * get files in folders and subfolders with $extensions extensions in $path.
 * @param array $extentios
 * @param string $path optinal. default is path of execution directory
 */
//default path is current directory and sub directories
function listFolderFiles($extensions ,$path = '.')
{
    //files to count line numbers sort in $files
    static $files;
    //extensions of files that you will count line numbers
    $extensions = ['php'];
    foreach (new DirectoryIterator($path) as $fileInfo) {
        if (!$fileInfo->isDot()) {
            if (in_array($fileInfo->getExtension(), $extensions)) {
                $files[] = $fileInfo->getPathname();
            }

            if ($fileInfo->isDir()) {
                listFolderFiles($fileInfo->getPathname());
            }

        }
    }
    return $files;
}

function counter($extensions, $path = '.')
{
    $counter = 0;
    $files   = (listFolderFiles($extensions,$path));

    foreach ($files as $key) {
        $counter = $counter + count(file($key));
    }
    return $counter;
}

//usage
echo counter(['php','css',], 'path/to/dir');