dir

<?php
 // simple juste use FilesystemIterator 
 // and you can skip dot and duble dot
 // and use it in array
 // new FilesystemIterator( PATH , OPTIONS ) : array 
$array_file_list = new FilesystemIterator( PATH_ROOT . 'folder/', FilesystemIterator::SKIP_DOTS );
?>

This one's pretty nice. After getting frustrated for hunting down .jpg files in my massive music collection (PHP would run out of memory), I thought there should be a preg_ls function.
function preg_ls ($path=".", $rec=false, $pat="/.*/") {
 // it's going to be used repeatedly, ensure we compile it for speed.
 $pat=preg_replace("|(/.*/[^S]*)|s", "\1円S", $pat);
 //Remove trailing slashes from path
 while (substr($path,-1,1)=="/") $path=substr($path,0,-1);
 //also, make sure that $path is a directory and repair any screwups
 if (!is_dir($path)) $path=dirname($path);
 //assert either truth or falsehoold of $rec, allow no scalars to mean truth
 if ($rec!==true) $rec=false;
 //get a directory handle
 $d=dir($path);
 //initialise the output array
 $ret=Array();
 //loop, reading until there's no more to read
 while (false!==($e=$d->read())) {
 //Ignore parent- and self-links
 if (($e==".")||($e=="..")) continue;
 //If we're working recursively and it's a directory, grab and merge
 if ($rec && is_dir($path."/".$e)) {
 $ret=array_merge($ret,preg_ls($path."/".$e,$rec,$pat));
 continue;
 }
 //If it don't match, exclude it
 if (!preg_match($pat,$e)) continue;
 //In all other cases, add it to the output array
 $ret[]=$path."/".$e;
 }
 //finally, return the array
 return $ret;
}
Not bad for a mere 18 lines, don't you think?
Example use:
foreach (preg_ls("/etc/X11", true, "/.*\.conf/i") as $file) echo $file."\n";
Output: 
/etc/X11/xkb/README.config
/etc/X11/xorg.conf-vesa
/etc/X11/xorg.conf~
/etc/X11/gui.conf
/etc/X11/xorg.conf
/etc/X11/xorg.conf-fbdev

Note that the dir object will use the default encoding for non-unicode programs on Windows with PHP 5.x.
So, if you have a file named with characters unsupported by the current default encoding, the dir->read() method will return a wrong entry.
<?php
/*
** This script is on the same directory than a file named with
** unsupported characters for the current default encoding.
*/
$d = dir("./");
while(false !== ($e = $d->read()))
 echo $e . '<br/>';
?>

This will print a "?" for every unsupported characters, and not the right file name. So take care if you check with is_file/is_dir right after enumerating.

<?php
/*
 New recursive PHP8 
 gen array path with FilesystemIterator
*/
$recurcive_path = [];
rdir(path, $recurcive_path);
var_dump($recurcive_path);
function rdir(string $path, array &$recurcive_path): string
{
 if ($path != '') {
 $recurcive_path[] = $path;
 $array_list = iterator_to_array(new FilesystemIterator($path, FilesystemIterator::SKIP_DOTS));
 foreach ($array_list as $name) {
 $pathname = $name->getpathname();
 if(is_dir($pathname) && $name->getfilename()[0] != '.'){
 $path = rdir($pathname,$recurcive_path);
 }
 }
 return $path;
 }
 return '';
}
?>

Regarding samuel's comment about the dir() function not supporting Unicode properly, it's all in the encoding. The function does NOT internally change Unicode characters into question marks (?), as I was first led to believe. If you simply try to output them in UTF-8, they'll show up just right.

to get a dir of http://www.example.com/directory
<?php
function remotedir($dir)
{
 $dir = str_replace(" ", "%20", html_entity_decode($dir));
 if (($rh = fopen($dir, 'rb')) === FALSE) { return false; }
 $i = 0;
 while (!feof($rh)) {
 $archivos = fgetss($rh);
 $directorio[$i++] = trim( substr($archivos,1,strpos($archivos," ",1)) );
 }
 fclose($rh);
 return $directorio;
}
?>