There was a saying that technology usually has inertia, if it was used for 30 years, and is used actively now, it will probably still be in use 30 years in the future.
I learned vim by necessity after shying away from this weird old tech for years, when I was forced to work on a solaris server where there was no other way to edit the code at all. It was pain and suffering for a few hours - we really wanted to fix something that day as I was working on a machine that we were “not allowed to ssh into” been driven to a different city in order to sit in front of it.
But after that day I’ve been using vim almost every day. It is not my daily driver, always felt more productive in TextMate, SublimeText and now VS Code, but it is still incredibly useful.
Any remote server I ssh into there is no question what I can or cannot do - can easily edit everything I want to. And I use it for various quick edit tasks in the shell.
Now learning shells wasn’t so dramatic for me but same rules apply, I don’t feel uncomfortable anywhere - that pod that is misbehaving in your cluster - well just ssh into it and poke around! You need to tie a few commands together as there isn’t something that does _exactly_ what your company needs - just whip up a quick bash script! - zero dependencies and can be deployed anywhere - your mac, the server the ci is running on, even windows machines!
So general rule is - if it was used for 50 years and is used now, it is probably worth learning.
I won't comment on which shell to learn, but you'll end up spending a lot of time in it, so learning your chosen shell well will pay off dividends for the rest of your life.
Shell scripting is incredibly powerful and omnipresent. So you want to know the basics about pipes, loops and the like.
But the language itself is broken by design (error handling is a mess; whitespaces create headaches daily; sub-shells can be a pain; ...). So, creating reliable scripts can be a challenge, and you do not want to become an expert on how to write large programs with the shell. Other languages, e.g. Python, are much better at this.
My favorite site in this context is https://shellhaters.org. It has a list of links to the POSIX standard so that you can easily look up functionality that is part of it (and should be present on all POSIX-compliant operating systems).
I also wonder. It didn't appear in my search because, I guess, it has too many features and the feature I want to search has a relatively low weight. I also searched x-cmd on HN but there aren't many positive comments... I would expect it's more popular on HN because it's written in POSIX shell and awk.
