fish

The Friendly Interactive Shell (fish) is a smart and user-friendly command-line shell for macOS, Linux, and other Unix-like operating systems. It features auto-suggestions, syntax highlighting, and clean configuration scripting.

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1. Installation

Ubuntu / Debian

# Add official PPA for the latest version
sudo apt-add-repository ppa:fish-shell/release-4
sudo apt update
sudo apt install fish -y

macOS

brew install fish

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2. Setting Fish as Default Shell

# Find the path of fish (usually /usr/bin/fish or /opt/homebrew/bin/fish)
which fish

# Add fish to valid shells list (if not already present)
echo (which fish) | sudo tee -a /etc/shells

# Change your default shell
chsh -s (which fish)

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3. Configuration & Startup Files

Unlike Bash or Zsh, Fish configuration is written in its own syntax and resides in:

• Main Configuration: ~/.config/fish/config.fish (Created manually if not present)
• Custom Functions: ~/.config/fish/functions/ (Files named <func_name>.fish are lazy-loaded automatically)

Adding Paths

# Add directory to $PATH (safely appends and checks for duplicates)
fish_add_path /opt/my-app/bin

Aliases vs. Abbreviations

Fish introduces abbreviations, which expand interactively as you type them in the terminal, keeping history clean.

# Define an alias (creates a wrapper function under the hood)
alias gs="git status"

# Define an abbreviation (expands to the full command when space is pressed)
abbr -a gd git diff
abbr -a gp git push

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4. Keybindings & Interactive Features

Fish has powerful interactive features out of the box.

Keymap	Action / Description
Tab	Open autocomplete suggestions (lists files, flags, command history)
Right Arrow or Ctrl + f	Accept the entire gray autosuggestion
Alt + Right Arrow or Alt + f	Accept only the next word of the autosuggestion
Up Arrow (after typing)	Search history for commands starting with what you typed
Ctrl + r	Search command history interactively
Alt + w	Show man page description for command under cursor

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5. Variables

Fish uses the set command to manage variables.

Scope & Export Controls

Command	Description
set var value	Set local variable (scope is the current block/function)
set -g var value	Set global variable (persists for the entire session)
set -x var value	Export variable (makes it visible to child processes)
set -gx var value	Set a global exported environment variable (similar to POSIX export)
set -e var	Erase / Delete a variable

Universal Variables

Universal variables are shared between all running Fish sessions and persist automatically across shell restarts without editing configuration files:

set -U EDITOR nvim

Lists / Arrays

Variables in Fish are lists by default. Note that indices are 1-indexed.

# Define a list
set my_list apple banana cherry

# Access items
echo $my_list[1]   # Output: apple
echo $my_list[-1]  # Output: cherry (last item)

# Append to list
set -a my_list date

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6. Fish Scripting & Syntax (vs. Bash/POSIX)

Fish syntax is designed to be clean and consistent, removing many quirks of POSIX shells.

Command Substitution

# Capture command output (POSIX: var=$(date) or var=`date`)
set current_date (date)

# Modern Fish (3.4.0+) also supports standard $() syntax
set current_date $(date)

Conditionals (If / Else)

# Use `test` to perform boolean evaluations
if test -f ~/.config/fish/config.fish
    echo "Config file exists"
else
    echo "Config file not found"
end

Logical Operators

# Fish uses explicit 'and', 'or', and 'not' keywords instead of &&, ||, !
git add .
and git commit -m "update"
and git push

Loops

# Loop through a list of values
for animal in cat dog bird
    echo "I love my $animal"
end

# Loop through files
for file in *.md
    echo "Processing file: $file"
end

Functions

# Define custom functions
function lsg
    # $argv captures all arguments passed to the function
    gls --color=auto --group-directories-first $argv
end

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7. Customization & Prompts

Web Configuration Tool

Fish comes with a built-in web-based config tool to customize colors, prompt, and keybindings visually:

fish_config

Custom Prompts

To define a custom prompt, create a function called fish_prompt in ~/.config/fish/functions/fish_prompt.fish:

function fish_prompt
    echo -n (set_color green)(prompt_pwd) (set_color normal)'> '
end