Prints out what shell you're using. Bash is default for most Linux distros. MacOS switched from bash to zsh as their default. Zsh is hella customizable, by default it functions more or less like bash.

Fish is cool, has neat quality of life features out of the box, but can also break scripts sometimes.

It's the index on 1 that ruins it for me.
Edit: come to think of it what would zsh print out for echo $0?

tbh it's fine and i use it a lot more than bash.

I went from bash to fish to zsh. I can see why people would like having fish as a shell. but I hated scripting on it and if I'm going to be triggering a different shell for scripts anyway, I might as well skip the middleman, not re-invent the wheel and just use zsh with plug-ins that way I only have two shells installed instead of three. Adding the auto-complete plugin and a theme plugin for zsh gives most of fishes base functionality and design while making it so I don't need to worry about compatibility.

Maybe someday when I'm less code oriented, I will re-look at fish, but I don't see it happening in the foreseeable future.

To me, it genuinely makes a huge difference that I don't have to manually press Ctrl+R for history search. Because 9 times out of 10, I accept a history suggestion from Fish where I did not think about whether it would be in my history.

This includes really mundane commands, like cd some/deeply/nested/path/. You would not believe, how often I want to cd into the same directory.
But I've also had it where I started typing a complicated docker run command and Fish suggests the exact command I want to write, because apparently I already ran that exact command months ago and simply forgot.