The php directory operates the example code

<?php 
    /**
    * listdir
    */
    header("content-type:text/html;charset=utf-8");
    $dirname = "./final/factapplication";
    function listdir($dirname) {
        $ds = opendir($dirname);
        while (false !== ($file = readdir($ds))) {
            $path = $dirname.'/'.$file;
            if ($file != '.' && $file != '..') {
                if (is_dir($path)) {
                    listdir($path);
                } else {
                    echo $file."<br>";
                }
            }
        }
        closedir($ds);
    }
    listdir($dirname);

Core: Classical application of recursion, and basic operation of files and directories.

<?php
    /**
    * copydir
    */
    $srcdir = "../fileupload";
    $dstdir = "b";
    function copydir($srcdir, $dstdir) {
        mkdir($dstdir);
        $ds = opendir($srcdir);
        while (false !== ($file = readdir($ds))) {
            $path = $srcdir."/".$file;
            $dstpath = $dstdir."/".$file;
            if ($file != "." && $file != "..") {
                if (is_dir($path)) {
                    copydir($path, $dstpath);
                } else {
                    copy($path, $dstpath);
                }
            }
        }
        closedir($ds);
    }
    copydir($srcdir, $dstdir);

Core: copy functions.

<?php
    /**
    * deldir
    */
    $dirname = 'a';
    function deldir($dirname) {
        $ds = opendir($dirname);
        while (false !== ($file = readdir($ds))) {
            $path = $dirname.'/'.$file;
            if($file != '.' && $file != '..') {
                if (is_dir($path)) {
                    deldir($path);
                } else {
                    unlink($path);
                }
            }
        }
        closedir($ds);

        return rmdir($dirname);
    }

    deldir($dirname);

Core: Note that unlink removes file with path.

<?php
    /**
    * dirsize
    */
    $dirname = "a";
    function dirsize($dirname) {
        static $tot;
        $ds = opendir($dirname);
        while (false !== ($file = readdir($ds))) {
            $path = $dirname.'/'.$file;
            if ($file != '.' && $file != '..') {
                if(is_dir($path)) {
                    dirsize($path);
                } else {
                    $tot = $tot + filesize($path);
                }
            }
        }
        return $tot;
        closedir($ds);
    }
    echo dirsize($dirname);

Core: Understand recursive functions by determining where $tot is returned.