A fin-troduction to fish

Table of contents

Introduction

enter fish!

…the friendly interactive shell. A shell is a program that starts other programs (you might have installed bash or zsh). fish offers a command-line interface that is focused on usability and interactive use1.

This introduction will be less about the syntax differences between the fish language and bash or zsh and more about the out-of-the-box features that are offered from this shell.

A dish served best straight out of the oven

Some of you might be familiar with zsh plugin managers such as oh-my-zsh that can configure zsh to your liking, but fish just works. No more messing with chunky zsh configs and slow shells that make you wait several hundred milliseconds to type another command.

Installation

It’s recommended to check the fish homepage for up-to-date instructions for installing the latest version of fish on your platform.

Syntax highlighting

fish performs syntax highlighting as you type. Invalid or non-existent, unexecutable commands appear red if they cannot be executed.

invalid-syntax-highlighting

On the contrary, valid commands will appear in a different color.

valid-syntax-highlighting

Autosuggestions

fish suggests commands as you type, based on command history. As you type commands, suggestions are offered after the cursor in gray. To accept the suggestion, press → or Control+F.

autosuggestions

Autocompletions

fish comes built with many autocompletions for commands you will encounter often. It also parses man pages and automatically generates completions.

autocompletions

Tab completion

Many shells offer tab completion, but fish provides a modern interface out of the box. When you type Tab, fish guesses the rest of the word under the cursor. It suggests a number of possibilities and opens a menu (or “pager”) that allows you to select the command you’re looking for.

tab

A Control+R for the future

This is a command that you might find yourself using a lot! In bash or zsh, to search your history, you can use Control+R to find some commands you’ve used previously. With fish, you can type a substring, such as ‘alac’, and press ↑ and ↓ (or Control+P and Control+N) to traverse commands in your history containing ‘alac’.

substr-updown

You can also use Control+R as usual and this opens a pager to search your history.

ctrlr

And for some privacy…

Prefixing the command-line with a space prevents the line from being stored in history. This can be useful if your command contains a secret token that you don’t want to be stored on disk.

Flying through directories

If you’ve ever used pushd or popd, you won’t have to ever again! Using Alt+→ or Alt+←, you can traverse through directories you’ve previously changed to.

A note on POSIX compliance

fish isn’t POSIX compliant, but it isn’t designed to be! Typing bash into the command-line to execute a command or running a script opening with a hashbang are always options if you need bash.

Default shell

At this point, if you’re convinced with the benefits of fish, you can change your login shell to it as follows:

  1. Add the shell to /etc/shells/:
echo /usr/local/bin/fish | sudo tee -a /etc/shells
  1. Change your default shell:
chsh -s /usr/local/bin/fish

Now, log out and log back in to see the changes in effect.

Plugins

First — yes, this post starts with saying fish works out of the box, and it does! You could stop right before this section and be happy with your new found shell.

But there’s just one plugin to fish to leave you with: Tide. Its most useful feature is that it enables asynchronous rendering, making the prompt instantly responsive.

Resources

References

  1. https://fishshell.com/docs/current/index.html ↩