This is how to list all files inside a directory and all subdirectories. Works well in browser and command line.

list_files.php

<?php

$is_cli = php_sapi_name() == 'cli';

/**
 * List all files inside a directory and all subdirectories.
 * 
 * @param  mixed  $directory
 * @param  bool  $is_cli
 * @return void
 */
function list_files($directory, $is_cli)
{
    $iterator = new DirectoryIterator($directory);

    foreach ($iterator as $item) {
        if (! $item->isDot()) {
            if ($item->isDir()) {
                list_files($directory . '/' . $item, $is_cli);
            } else {
                echo $directory . '/' . $item->getFilename() . ($is_cli ? "\n" : '<br>');
            }
        }
    }
}

list_files(__DIR__, $is_cli);