ZSH has been my shell of choice since I started my command-line-centric workflow. It’s a popular shell with a large community and an unprecedented level of customizability. ZSH is also POSIX-compliant, which was very important to me for some reason. However, after some reconsideration, I decided to port my config to the Fish shell, and this is why.

Performance

Performance is the price you have to pay for flexibility, and for a while it felt that the customizability and features of ZSH were worth it. But recently, I noticed that I frequently started typing before ZSH was fully loaded. I decided to benchmark the start-up time ZSH compared to 2 other shells, namely Fish and Nu. Because these shells are on par with my customized ZSH by default, it’s fair to compare them that way. Here is the result:

I’m surprised that Fish is almost 4 times faster than ZSH, and can start up (and exit) in less than 1/60 of a second, which is faster than the refresh rate of my monitor. This is a great result, while start-up time doesn’t accurately reflect the shell’s responsiveness during interactive usage, it is usually a good enough indicator. There have been many reasons for me to switch to Fish, which I will discuss below, but the performance benefit is the final nail in the ZSH coffin.

Fish features

Out-of-the-box, Fish is already packed with many useful features, such as syntax highlighting, autosuggestions, and prompts with git integration. They worked so well that I didn’t have to install any extensions. Of course, ZSH has all these features, but they are not built-in, so they probably contributed to the performance difference we observed earlier.

Other than that, there are some features that feel “nicer” in Fish, such as vi mode and completion menus, and I consider good performance to be a feature in and of itself. Fish also has sensible defaults, which shrunk the size of my configuration file, and fewer configurations means less worrying about messing up somewhere.

Non POSIX-compliant

Another selling point of Fish is its syntax, which took its own turn away from the POSIX standards. Although I find the syntax much nicer than POSIX- compliant shells, I won’t use it for anything other than writing my Fish config. If I care about portability, I’d use regular shell scripting. Otherwise, I’d use something like Python, Deno, or even Nu.

The non-compliancy extends beyond scripting and also affect interactive use. This, compared with the fact that you can get all of Fish’s features with a configured ZSH, is why I’ve been staying away from Fish. However, I’ve been adopting modern, non-standard alternatives, from programming style, paradigm, languages, to softwares that I use. I’m starting to see that while standards have their values, they are also limitations that sometimes you have to break free to reach new heights.

Drawbacks of using Fish

Because Fish is not as configurable as ZSH, there are things that I’d like to change but are impossible to do. For example, I like autosuggestions, but don’t like using my history as a source, and there’s currently no option to configure that. I’m also used to being able to use vim keybindings on the tab completion menu, and there’s no way (that I know of) to enable it in Fish. However, I can work around these problems, and other Fish features make dealing with them worth it.

Being non-POSIX-compliant also means that you’re relying on shell-related applications to support Fish. For example, to activate Python virtual environments, I have to execute {path-to-env}/bin/activate.Fish instead of {path-to-env}/bin/activate. If the maintainer doesn’t care to maintain the Fish version of the script, I’m effectively on my own. There might be many other intricacies of using Fish instead of a POSIX-compliant shell, and so far I haven’t encountered any of them.

What about Nu

Nu is another modern, non-standard shell, which offers a unique approach to working with your terminal. From my understanding, Nu adds data types to its language instead of just working with raw textual data. There are also pipelines, which enable powerful data manipulation. Its syntax and error messages also make scripting in it much better than other shells or even programming languages.

However, Nu is still changing quite often, so it’s probably not a good idea to use it as an interactive shell. While the structured data is good for manipulation, Nu failed to display it in a way that look as good as regular textual output, at least to me. Also, since most UNIX command-line tools operate on plain text, I doubt that Nu will work well in cases involving third-party tools.

I think that Fish is a better general-purpose, interactive shell. However, I’m still open to the idea of switching completely to Nu in the future. Until then, I still keep Nu around for data manipulation and scripting. Also, if I ever use Windows on any of my machine, I’ll use Nu as an interactive shell there. Nu is great, and I recommend everyone to check it out.

Final thoughts

So after more than 2 years, I finally migrated from ZSH to Fish. I’m still amazed at how quickly my shell instances start up now. As of the time of writing, I’ve partly gotten used to Fish’s syntax differences in interactive use, and completely ported my old ZSH config. I’m enjoying the benefits of using Fish already, but only time will tell if Fish behaves well along the road.