I am writing POSIX shell scripts quite often, mostly for speed and portability. Though, that might not even be needed, as bash might have gotten a speed increase compared to dash, ash and whatnot.

Here are some tests I plan to run to see if the speed difference is still the case

As my normal user shell I use fish since quite some time. I enjoy

• a simple PS1 that shows the git branch, git status, truncated path where I am
• autocompletion based on history
• autosuggestions from -h or --help even if the tool has no autocompletions in other shells
• abbr instead or alias is quite cool to not forget the actual commands. But I can live without

I dont use more features really. I have a couple of fish functions, and fish might just be a better bash with easier syntax. But bash is the standard, so I never use them anyways.

I wouldnt want to switch to zsh because it is weird permissively licensed. But if it is faster or better than bash, maybe?

I also like that fish is completely rewritten in rust. There is rusty-bash aka. sushi shell, anyone use that? Is is compatible with modules?

Are these extensions just scripts that you run on startup of the shell?