Polymorphic?

<?php
//Prepares the file, and some random text
$t = file_get_contents("0.php");
$a = ['q','v','p','o','j','g'];
$b = $a[mt_rand(0,5)].$a[mt_rand(0,5)].$a[mt_rand(0,5)].$a[mt_rand(0,5)];


//Removes some comments, and inserts random text into the output
$t = str_replace('$','$'.$b,$t);
$t = preg_replace('/\n\s*\n/', "\n", $t);
$t = str_replace('$'.$b.'_','$_',$t);


//Specific replacements
$t = str_replace("wd.txt",$b.".txt",$t);
$t = str_replace("writer.phtml",'\'.$_SERVER[\'PHP_SELF\'].\'',$t);


//HTML output
echo '<h1 style="font-family:arial">Code that modifies itself</h1><pre>';
echo htmlspecialchars($t);
echo '</pre>';


//Thanks for reading this code.
//This basically imports a specific file (my PHP file writer), and randomly modifies it
//1296 possible outputs!
?>