Only drawback is that it's not POSIX, no issue for me, but maybe for people who have a lot of muscle memory with bash.
Later I found fizsh, which I love and still use as default shell now. It's basically a configuration around zsh adding the colors, completions, and other good stuff inspired by fish to zsh. Can really recommend it for those who are used to zsh or bash but want their CLI to be more readable. Colors especially help with big command line arguments to show where they start and end, and keeping track of complex stuff like loops and conditional logic in your commands.
Fish is nicer to script in by far, and you can keep those isolated with shebang lines and still run Bash scripts (with a proper shebang line). The only thing that’s tricky is `source` and equivalents, but I don’t think I’ve ever needed this in my main shell and not a throw-away sub shell.
I guess that somewhat breaks with fish: either you use bash -c '...' from the start, or you adopt the fish syntax, which means you need to convert again when you switch to a (bash) script.
I also don’t trust myself to not screw up anything more complex than running a command on Bash, without the guard rails of something like shellcheck!
First, there are some ways to make fish more compatible with bash.
If you want to do some shell scripting in fish, or running other people's shell scripts (or commands) this may aid you since you wouldn't have to port them (or take less time to port them over).
You can achieve this with a plugin system such as 'oh my fish' or 'fisher'. But, as always, it adds complexity (and bloat :P), you'll need it on every fish shell (including remote systems), etc.
It is a bit akin to having nvim with plugins versus being able to use vi. Sometimes, you're going to need to be able to use the latter.
Also, to people who recently adopted fish: fish has been made more and more compatible with bash throughout those years.
FWIW, I use fish with starship these days.
and script.sh just starts with #/bin/bash
I'm simple
Shell scripts from third parties stick with whatever shell they were written for (ie. /bin/sh or /usr/bin/env bash), and commands copy/pasted from the internet are either quickly executed with bash (one-off) or ported over. Because I like to have such in my history (fish is configured to use atuin), I want to keep using the same shell, so I try to stick with fish. If I cannot convert a command (usually a bunch of commands) to fish, it is PEBCAK and a learning curve/experience.
As for tmux, that is solid advice, because it also allows to stick with a shell which is known to work. I've come to like zellij with alacritty, with zellij the option is default_shell. But now that I use ghostty, I don't use a terminal multiplexer locally any more; only remotely. And there I still use tmux.
