I've been trying to "upgrade" one of my scripts from the now-outdated (so I am told) CGI.pm to a more modern implementation that I had hoped would be mostly a "drop-in" replacement for it: CGI::Tiny.

What portion of the CGI::Tiny documention said to you "drop-in replacement"? Looking at that documentation, compared to my CGI.pm experience, it seems a completely different philosophy.

Something like CGI::Simple, on the other hand, specifically says as the first sentence of the DESCRIPTION: "CGI::Simple provides a relatively lightweight drop in replacement for CGI.pm." It has all the parameter-handling interface, without any of CGI.pm's poorly-designed and deprecated HTML-generating code.

• If your goal is a drop-in replacement, I would suggest going with CGI::Simple (or just using the non-HTML portions of CGI.pm -- because while the HTML generation portion is deprecated, and the whole module is now non-core, CGI.pm and the Common Gateway Interface it implements still works and is still available and useable); then you can spend your learning-effort in something like Template Toolkit for improved HTML generation, instead of learning a new philosophy for handling the parameters and everything.

• If you want to learn something new and different on the interface side, then CGI::Tiny might do it; but looking briefly at its documentation, I would not have come up with a SSCCE like hippo was able to do here, so it might not have the easiest learning curve for someone who still has the CGI.pm thought processes...

• But if you're going to bother trying to learn a whole new philosophy anyway, why not go with one of the "big 2" rather than CGI::Tiny , which I have rarely-if-ever remembered seeing mentioned here. For me, when I tried to expand my horizons a couple years ago, I was able to learn from the Mojolicious::Lite documentation sufficiently to get apps of similar complexity to the ones I used to do in CGI.pm, so that is what I personally use when doing a new script for my hobby website; I am not an expert by any means, but I can get some simple endpoints. (Something that I don't think is clear enough in their docs: if you have an old-fashioned CGI-based web host, like many of the shared hosts out there, you don't need to do any of their fancy stuff with the "server" side of things; you just put your Mojolicious::Lite-using script in your cgi-bin folder or wherever you used to put it with a CGI.pm-based app, and it will work the same.)

CGI::Alternatives does a really good job of showing you an old style CGI+HTML-from-CGI.pm, then showing you the equivalent application in CGI.pm+TemplateToolkit (which would be virtually identical to CGI::Simple + Template Toolkit if you wanted to go down that path), and then in Mojolicious::Lite, Mojolicious "full", and Dancer2.