Can you recommend any free resources that amount to an "effective minimal core" or crash course for Perl? I'M a Python dev, but I use sed/cat a great deal, and maybe Perl is a better solution. (Take me to the Dark Side.)
I picked up a bunch of info from perl.org: https://perldoc.perl.org/perl#Tutorials
Perlmonks was a good source for certain specifics.
Doing is better than reading IMO. Open files, parse log data or such with regexes, sort them into a hash, and return that by reference. Perl has different ways of doing things that aren't common in some languages such as how it deals with binary data (see pack/unpack).
Coming from python, I would say forego the delving into OOP aspect of perl as it is more of an afterthought than a core feature. Focus on understanding data management with scalars, lists, hashes, and the core functions (Perl has native functions for things like sorting which are quite useful).
I managed to go from C to perl over a weekend but it takes hours of practice to improve.
It is dated but it's free online:
http://modernperlbooks.com/books/modern_perl_2016/index.html
I personally learn by practice. Writing stuff. I've read good things about the "Modern Perl" but I'll check out Conway if people here are vouching for it. Also, Perl's manpages actually teach you the language - another advantage of an older language from a time when people knew what manpages were and how to write them. They're not OpenBSD quality, but they're pretty good from my experience.
For me, going through the llama book (Learning Perl) and actually doing the exercises was great. I would think I got it after reading the chapter, but when I went to do the exercise, I realized I had to look up the info again. Putting it into practice was great for internalizing the information. I can't believe there's an 8th edition now (from 2021!). I must have used the 2nd edition (1997) at the most, so I'm assuming it's still good.
Since you know sed/awk, you're going to see where a lot of the ideas came from.