Continuously expanding code
PHP, 100

More efficient, 101

&lt;?$a=$argv[0];$b=file_get_contents($a);file_put_contents($a,$b.substr($b,81,20));echo"Hello World\n";


This script is appending an echo"Hello World";, but because you said the size should also vary, and because it's shorter, I'm also having this script:

Shorter, 100

&lt;?$a=$argv[0];$b=file_get_contents($a);file_put_contents($a,$b.substr($b,2,98));echo"Hello World\n";


This script is appending itself, in a way it adds one Hello World, but this version will overall take more space and takes longer to execute.

Example

But the scripts don't vary when it comes to the output:

root@raspberrypi:~/stack# php hello_expand.php
Hello World
root@raspberrypi:~/stack# php hello_expand.php
Hello World
Hello World
root@raspberrypi:~/stack# php hello_expand.php
Hello World
Hello World
Hello World