PHP Script for Tiki Wiki

So I have the following code:

export RND=$(echo ${RANDOM:0:4})&&export MDATE=$(echo `date`)&&perl -i.bak -pe 's@.*Incony.*$@\<\!--    Incony AG Webmail Service $ENV{"MDATE"}:$ENV{"RND"}          --\>@' /srv/www/htdocs/H3.1/horde/templates/common-header-sidebar.inc

I would like to "import" this code to the Tiki Wiki from an older workspace to generate a 4 digit long random number every month. How do I do this? I am kinda stuck right now.. maybe create a new plugin?