List Files deeply

gistfile1.php

<?php 

function files($dir, $callback) {
    $queue = array($dir);
    $r = -1;
    $w = 0;

    while ($r < $w) {
        $path = $queue[++$r];
        
        $dir = dir($path);       
        while (FALSE !== ($entry = $dir->read())) {
            if (FALSE !== strstr('..', $entry)) continue;

            $entry = $path . DIRECTORY_SEPARATOR . $entry;

            if (is_dir($entry)) {
                if (is_executable($entry)) {
                    $queue []= $entry;
                    $w++;
                }
            } else {
                $callback($entry);
            }
        }
        $dir->close();
    }
}

files('/etc', function ($file) {
    echo $file, PHP_EOL;
});