there are not enough of them now, they used to be more prevalent
StackOverflow is Internet Age help
ChatGPT is post-Internet Age help
In ascending order of helpfulness (modulo LLM confabulation)
ChatGPT inherited "confidently wrong" and "misunderstanding question and then answering to question they misunderstood" from stackoverflow
Actually, this seems to be a case where chatgpt is smarter than the humans.
As of now, there is no LLM without confabulation, so your third item is effectively "hypothetical fantasy ChatGPT that we hope will be available some time in the future", not the actual tools we have right now.
The resulting command looked good at first sight, something like „mkvmerge -o output.mkv first.mkv —-no—video -s 1 -a 2 -a 3 -a 4“. The problem here is that there can only be one -a flag, so it should have been „-a 2,3,4“ instead. But mkvmerge didn’t really care and just discarded every -a flag except the last one. So I ended up with only one of the audio tracks copied over. I only noticed when I actually checked the resulting file that it had less audio tracks than it was supposed to.
This would not have happened to a human after studying the man page - the documentation is very clear about the -a flag and I have no idea what led ChatGPT to come to the conclusion it did.
Learning to program for example Perl. I had the learning book, the reference book and the cookbook. learning I did once, the reference had post its on it and was on my work desk. The cookbook was more the facebook type you read it on the toilet.
They had books on everything that were the industry standard. DNS, Apache, Javascript, ... The revised them regularly. For Js had the 1st, 2nd, 3rd edition. I know this sounds all ancients like real paper books. But even work had O'reilly subscription so you could order what you need.
For me it was O'reilly books, man pages. But lets not forget when you installed Linux like RedHat (not fedora yet) you could install the linux howtos. Oh boy did I learn a lot from them too: https://tldp.org/HOWTO/HOWTO-INDEX/howtos.html
Finally there was IRC if you were stuck but this was off course the internet stage. I just went online to ask a question, dialup was expensive ;)
i've been using https://git.causal.agency/exman/about/ to compare linux and bsd manpages, and it has saved me an incredible amount of time looking things up.
Ironically, this sort of stuff -- the basic conventions like qhjkl0^$G + CRFFBSSPC keyboard navigation and :/? prompt modes -- is exactly what one initially learns from guides, tutorials, other people in IRC, and whatnot, long before coming to reference doco. The _Introduction to Linux_ book at TLDP covers the bare essentials of these conventions, q, b, and SPC, in the "quickstart" chapter 2.
For emacs stuff, yes, it's very convenient. I remember once upon a time, Python docs were available in info as well. When you have good documentation available in info, it's very nice.
While this attitude made sense pre-internet, reading about every switch for common use cases is just not realistic today. Maybe if the number of command-line programs were less, and the complexity of each command was significantly less, I could see how it would be done, but not today.
Maybe 30 years ago you could learn through manpages but today that's how all the man pages of all the useful commands look. If you think grep is nice it would be the exception; for me it is indeed short, simple and easily searchable, but too terse for a beginner to learn with easily. (Plus even the regex documentation only documents grep mode, not egrep or pgrep or anything else.) Very useful in its own way, but most man pages are useless for learning.
I am disappointed at how few man pages take the opportunity to have a useful selection of "the 10 most popular things to do with this command" but web search has filled in reasonably decently. You do still have to understand the basics of how shell works, though, because most of them aren't quite what you want today and honestly a fair number of them aren't even what the poster thought they were. I am also in the habit of making sure that I understand every command line switch before I copy & paste a command off the internet, again, because many of them aren't what you need today. I don't always mean in a malicious manner, but things like either do or do not follow HTTP redirects in curl may or may not matter to you today, but the poster may be in the habit of setting it one way or another for no reason relevant to you.