Find invalid filenames from a web host

With the following code, you can find invalid filenames under a directory:

<?php
// change according to your needs
$dir = __DIR__;

// force browser to show the output as plain text
header('Content-Type: text/txt; charset=utf-8');

// scan directory
$dir = new DirectoryIterator($dir);
foreach ($dir as $fileinfo) {
    // do not process . and ..
    if ($fileinfo->isDot()) {
        continue;
    }

    $filename = $fileinfo->getFilename();

    if (strlen($filename) == strlen(utf8_decode($filename))) {
        continue;
    }

    // filename mismatch
    echo $dir . $filename . "\n";
}

Obviously, to be used on a php web host.