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Playing with a new shell: fish

Author: Solène
Date: 05 September 2021
Tags: openbsd shell

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Introduction

Today I'll introduce you to the interactive shell fish. Usually, Linux distributions ships bash (which can be a hidden dash, a limited shell), MacOS is providing zsh and OpenBSD ksh. There are other shells around and fish is one of them.

But fish is not like the others.

fish shell project website

What make it special?

Here is a list of biggest changes:

suggested input based on commands available
suggested input based on history (even related to the current directory you are in!)
not POSIX compatible (the usual shell syntax won't work)
command completion works out of the box (no need for extensions like "ohmyzsh")
interconnected processes: updating a variable can be done into every opened shells

Asciinema recording showing history features and also fzf integration

Making history more powerful with fzf

fzf is a simple utility for searching data among a file (the history file in that case) in fuzzy mode, meaning in not a strict matching, on OpenBSD I use the following configuration file in ~/.config/fish/config.fish to make fzf active.

When pressing ctrl+r with some history available, you can type any words you can think about an old command like "ssh bar" and it should return "ssh foobar" if it exists.

source /usr/local/share/fish/functions/fzf-key-bindings.fish
fzf_key_bindings

fzf is absolutely not related to fish, it can certainly be used in some other shells.

github: fzf project

Tips

Disable caret character for redirecting to stderr

The defaults works pretty well but as I said before, fish is not POSIX compatible, meaning some habits must be changed. By default, ^ character like in "grep ^foobar" is the equivalent of 2> which is very misleading.

# make typing ^ actually inserting a "^" and not stderr redirect
set -U fish_features stderr-nocaret qmark-noglob

Web GUI for customizing your shell

If you want to change behaviors or colors of your shell, just type "fish_config" while in a shell fish, it will run a local web server and open your web browser.

Validating a suggestion

When you type a command and you see more text suggested as you type the command you can press ctrl+e to validate the suggestion. If you don't care about the suggestion, continue typing your command.

Get the return value of latest command

In fish, you want to read $status and not $? , that variable doesn't exist in fish.

Syntax changes

Because it's not always easy to find what changed and how, here is a simple reminder that should cover most of your needs:

loops (no do keyword, ends with end): for i in 1 2 3 ; echo $i ; end
condition (no then, ends with end): if something ; echo true ; end
inline command (no dollar sign): (date +%s)
export a variable: set -x EDITOR kak
return value of last command: $status

Conclusion

I love this shell. I've been using the shell that come with my system since forever, and a few months ago I wanted to try something different, it felt weird at first but over time I found it very convenient, especially for git commands or daily tasks, suggesting me exactly the command I wanted to type in that exact directory.

Obviously, as the usual syntax changes, it may not please everyone and it's totally fine.