$ Linux Command

Processes

fish

The Friendly Interactive Shell.

shellterminalfishautosuggestioncompletion

Additional Notes

Fish is a modern command-line shell designed with user-friendliness as a primary goal. Unlike bash or zsh, fish requires no configuration for basic features: it provides syntax highlighting, autosuggestions, tab completions, and a web-based configuration interface out of the box. It is not POSIX-compliant, meaning bash scripts may need adaptation to run under fish.

Key design differences from bash include: no ~/.bashrc or ~/.profile (fish uses ~/.config/fish/config.fish), a different scripting syntax (e.g. if test -f file instead of if [ -f file ]), and functions being the primary means of defining commands.

Syntax

fish [options] [file] [arguments]

Parameters

  • file: A script file to execute. If no file is given, fish runs interactively.
  • arguments: Arguments passed to the script or interactive session.

Common Options

  • -c command: Run the specified command(s) and exit.
  • -i: Force interactive mode.
  • -l, --login: Run as a login shell.
  • -n, --no-execute: Parse but do not execute commands (syntax check).
  • -N, --no-config: Do not load configuration files.
  • -v, --version: Show version and exit.

Features

  • Autosuggestions: Fish suggests commands as you type, based on history and completions. Accept with Ctrl+F or right arrow.
  • Syntax highlighting: Commands are colorized as you type: valid commands in blue, invalid in red, options in cyan, etc.
  • Tab completions: Extensive completions for many commands, generated from man pages.
  • Web configuration: fish_config opens a web UI for themes, prompts, and settings.
  • Prompt: A friendly, informative prompt with git integration out of the box.
  • Functions: The primary way to define commands. function name; body; end.
  • Universal variables: Variables shared across all fish sessions.

Examples

fish

Start an interactive fish shell.

fish -c "echo Hello"

Run a command with fish without entering an interactive shell.

fish script.fish

Execute a fish script.

fish -n script.fish

Check syntax of a fish script without executing it.

fish -N

Start fish without loading user configuration.

fish_config

Open the web-based configuration interface.

Configuration

Fish reads configuration from ~/.config/fish/config.fish. Key directories:

  • ~/.config/fish/config.fish: Main configuration file.
  • ~/.config/fish/functions/: Directory for automatically loaded functions.
  • ~/.config/fish/completions/: Directory for custom completions.
  • ~/.config/fish/fish_variables: Stores universal variables.

Example config.fish:

set -gx PATH $PATH ~/.local/bin
set -gx EDITOR vim
alias ll "ls -lah"
starship init fish | source

Practical Notes

  • Fish is not POSIX-compliant. If you need strict POSIX compatibility, use bash or dash.
  • Switch between fish and bash temporarily with bash or exec bash.
  • To make fish your default shell: chsh -s $(which fish).
  • Many bash-specific syntax elements (like $(()), [[ ]], export) do not work in fish. Use set -x, test, and set -gx instead.
  • The fisher plugin manager adds easy plugin installation.
  • Fish's scripting language is cleaner than bash but less portable; scripts written in fish will not run in other shells.