Thank you, choroba, for your solution.

(I was able to run it on my Strawberry Perl installation.)

I learned about the Template module, the front-end module to the Template Toolkit.

I also learned about *DATA{IO}, which apparently points to the data below the special literal __DATA__.

I used Super Search and found the Using the DATA file handle for ARGV Perl Monk Meditation. This cleared up my questions about the special literal __DATA__ values IO slot, *DATA{IO}, of the *DATA typeglob.