[TYPO3-dev] How do I compare multiple files using diff?

[Christopher]

Hi guys,

at the moment I am using the following line to compare differences between 2 
files:

<?php
exec("diff -u $oldFile_1 $newFile_1 > $output_1");
?>
(I don't have shell-access available.)

Now I want to compare twice two files or three times two files (not whole 
folders!) AND want the result in just ONE otput file.
How do I achieve this?
-- 
Christopher