We have templates that use the variable script_name for the path and filename of the script that called them, particularly as the action attribute of forms that call back to it.

We have scripts that set the template->param script_name to their path and filename.

What we don't have is a 1:1 match between templates and scripts, as the failure mode in bug 37797 comment 1 shows. If you set action="[% script_name %]" when it isn't defined, you get action="", which may work for years if every form submitted to that script is a POST, but once someone changes one to a get, action="" will POST to aqbudgetperiods.pl?op=delete_confirm&budget_period_id=2 and both the things in the POST body and also things in the query string will wind up being sent to the script.

What I don't have is any good idea how to find templates using unset script_name, short of just brute force looking at every one.