Quick and dirty rename of all files of one file extension to another (in this case, .html.php to .phtml)

rename.php

<?php

$objects = new RecursiveIteratorIterator
(new RecursiveDirectoryIterator(__DIR__),
    RecursiveIteratorIterator::SELF_FIRST);

foreach ($objects as $path => $fileObject) {

    $use = true;
    $file_name = '';
    $base_name = '';

    if (is_dir($fileObject)) {

        if ($fileObject->getFileName() == '.' || $fileObject->getFileName() == '..') {

        } else {

            $path = $fileObject->getPathName();

            foreach (scandir($path) as $filename) {
    
                if ($filename == '.' || $filename == '..') {
                } else {
                    $newname = preg_replace('"\.html.php"', '.phtml', $filename);
                    rename($path . '/' . $filename, $path . '/' . $newname);
                }
            }
        }
    }
}

Thanks again, @peterjmit