fish

# Fish (Friendly Interactive Shell) Fish (Friendly Interactive Shell) is a smart, user-friendly command-line shell featuring autosuggestions, syntax highlighting, and clean scriptable syntax out of the box. ## When to Use - **Interactive Developer Shell**: Out-of-the-box autosuggestions, syntax highlighting, and tab completions without plugins. - **Clean Shell Scripting**: Intuitive scripting syntax without legacy POSIX quirks (no subshells for math, clear array handling). - **Custom Universal Variables**: Persisting user variables (`set -U`) across all shell sessions without editing config files. - **High-Speed Shell Startup**: Instant startup times (< 20ms) without heavy plugin manager overhead. ## Quick Start ```fish # Define and persist a custom function in Fish function mkcd --description "Create directory and cd into it" mkdir -p $argv[1]; and cd $argv[1] end # Save function permanently funcsave mkcd ``` ## Core Concepts ### Modern Shell Configuration (config.fish) Configuring environment, completions, and aliases: ```fish # ~/.config/fish/config.fish if status is-interactive # Disable default greeting set -g fish_greeting "" # Modern path exports fish_add_path /opt/homebrew/bin $HOME/.cargo/bin $HOME/.local/bin # Environment variables set -gx EDITOR nvim set -gx KUBECONFIG $HOME/.kube/config # Fast shell abbreviations (expanded automatically on Space/Enter) abbr -a g git abbr -a gco git checkout abbr -a k kubectl abbr -a d docker abbr -a tf terraform # Initialize Starship prompt if installed if command -q starship starship init fish | source end end ``` ### Clean Fish Scripting Syntax Writing readable, modular functions and loops: ```fish # ~/.config/fish/functions/deploy_service.fish function deploy_service --description "Build and deploy service container" set -l service_name $argv[1] if test -z "$service_name" echo "Error: Service name argument required" return 1 end echo "Deploying $service_name to production cluster..." docker build -t "myregistry.com/$service_name:latest" . and docker push "myregistry.com/$service_name:latest" and kubectl rollout restart deployment/$service_name if test $status -eq 0 echo "Deployment completed successfully!" else echo "Deployment failed with exit code $status" end end ``` ### Universal Variables (set -U) Setting variables across all current and future shell sessions instantly: ```fish # Persist variable globally across all fish sessions without writing to config.fish set -U FZF_DEFAULT_OPTS "--height 40% --layout=reverse --border" ``` ## Common Patterns ### Universal Environment Variables and Custom PATH **Problem**: Exported environment variables lost when closing shell session in bash/zsh. **Solution**: Use Fish universal variables (`set -U`): ```fish # Set once; persisted across all shell sessions and reboots permanently set -U EDITOR nvim set -U fish_user_paths /opt/homebrew/bin $HOME/.cargo/bin $fish_user_paths ``` ## Best Practices **Do**: - Use `fish_add_path` to add directories to `$PATH` idempotently without duplicates. - Use abbreviations (`abbr -a`) rather than aliases; abbreviations expand in place, maintaining transparent history. - Wrap interactive configurations inside `if status is-interactive ... end` to keep non-interactive script startup instant. - Store standalone functions in `~/.config/fish/functions/<name>.fish` for automatic lazy loading. **Don't**: - Write system administration shell scripts in Fish if POSIX `/bin/sh` or `/bin/bash` portability is required. - Use legacy bash syntax (e.g. `export FOO=bar` or `$(command)`); use `set -gx FOO bar` and `(command)`. - Overload `config.fish` with heavy external subshell calls; benchmark startup with `fish --profile`. ## Troubleshooting | Error | Cause | Solution | | :------------------------------------------- | :------------------------------------------------ | :---------------------------------------------------------------------------- | | `fish: Unknown command: source .../activate` | Sourcing bash virtualenv script into Fish shell. | Source the fish-specific activation script: `source .venv/bin/activate.fish`. | | `export: command not found` | Attempting POSIX `export VAR=val` syntax in Fish. | Use Fish syntax: `set -gx VAR val`. | | `&& operator syntax error in legacy Fish` | Using `&&` in older Fish versions. | Upgrade to Fish 3.0+ or use `; and` operator. | ## References - [Fish Shell Documentation](https://fishshell.com/docs/current/index.html)