List all files in and under the specified directory.

list-all-files.php

<?php
header("Content-Type: text/plain");

$root = './wp-content/uploads';
// From: https://stackoverflow.com/a/24784020/8605943
$rii = new RecursiveIteratorIterator(new RecursiveDirectoryIterator( $root ));

$files = array(); 

foreach ($rii as $file) {
    if ($file->isDir()){ 
        continue;
    }
    $files[] = $file->getPathname(); 
}

echo implode( "\n", $files );