PHP get all files in DIR

My question stem form an old one I asked a while back.
OLD Question

In the code below I am trying to change the first line  Into code that will get all the files in a DIR
and run the rename script on each of them.

Exact file names are unknown.

Any help is appreciated.
Thank you

Selvol

<?php
$str = file_get_contents("a.php");
        preg_match('%<meta name=\"keywords\" content=\"([^"]*)"%i',$str,$matchArray);
        $namesArray = explode(",",$matchArray[1]);
        $file = fopen($namesArray[0].$namesArray[1].$namesArray[3].".txt","w+");
        fwrite($file,$str);
        fclose($file);
?>

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