Delete or replace first line of 3500 php files

Question

I have an old server, all php files are compromised by a malicious code on the first line of all files. I would replace the first line by a simple line that contains <?php

could you advise me a linux command for doing this ?

thank you

Answer 1

I write this :

    grep 'create_";global' -rl | xargs sed '1 s/^.*$/<?php/g' -i

and I think it doing the job