How to write a Self Replicating Worm in PHP

Mar 28, 2020 · 1 min read

Self replicating code is a fun coding exercise to flex the old brain muscle.

Here’s an example of a self replicating worm program, written in PHP.

<?php
$selfReplicatingCode = <<<'EOL'
<?php
$selfReplicatingCode = <<<'EOL'
%s
%s
// The worm copies itself to another file
$copy = tempnam(__DIR__, __FILE__);
file_put_contents($copy, file_get_contents(__FILE__));
printf($selfReplicatingCode, $selfReplicatingCode, "EOL;");
EOL;
// The worm copies itself to another file
$copy = tempnam(__DIR__, __FILE__);
file_put_contents($copy, file_get_contents(__FILE__));
printf($selfReplicatingCode, $selfReplicatingCode, "EOL;");

Basically the worm copies itself into another random file stored somewhere in your /tmp directory. It doesn’t do anything useful or malicious. Just for learning purposes.