I had to get re-aquainted with virtual hosts, so your suggestion was really helpful in eventually finding my mistake. I am on my laptop using this as a local test and completely forgot set up /etc/hosts file.

I was just accessing everything via the full local url, eg http://127.0.0.1/projectsite/public_html/test.pl. I set up a virtual hosts with a proper server name locally ( eg projectsite.local ) then added this to my hosts file, it was all honky-dory. Part of my confusion was the assumption that mod_perl and mod_php work the same way - php works without having to set up a virtual host this way. But I found digging into virtual hosts a useful learning experience.

thanks for your feedback, I lead me to the solution!