fishshell

A smart and user-friendly shell, better than bash.

Installation

# Ubuntu and Debian installation:
sudo apt-get install fish

# macOS installation:
brew install fish

Startup and Help

Since Fish syntax differs significantly from Bash, Bash scripts are generally not compatible. It is recommended not to set Fish as your default shell immediately; instead, start it manually when needed.

# Start Fish after installation:
$ fish

# To get help while using Fish:
$ help

Color Display

# Invalid commands are shown in red:
$ mkd

# Valid commands are shown in blue:
$ mkdir

# Valid paths are underlined. If there's no underline, the path does not exist:
$ cat ~/somefile

Autosuggestions

Fish automatically provides suggestions behind the cursor in grey. To accept a suggestion, press → or Control + F. To accept only the first part of the suggestion, press Alt + →.

$ /bin/hostname      # Command suggestion
$ grep --ignore-case # Parameter suggestion
$ ls node_modules    # Path suggestion

Auto-completion

When typing commands, Fish automatically shows matching entries from your history. If no history match is found, Fish guesses the possible results. For example, typing pyt and pressing Tab will autocomplete to the python command.

Fish also supports auto-completion for Git branches.

Scripting Syntax

if Statement

if grep fish /etc/shells
    echo Found fish
else if grep bash /etc/shells
    echo Found bash
else
    echo Got nothing
end

switch Statement

switch (uname)
case Linux
    echo Hi Tux!
case Darwin
    echo Hi Hexley!
case FreeBSD NetBSD DragonFly
    echo Hi Beastie!
case '*'
    echo Hi, stranger!
end

while Loop

while true
    echo "Loop forever"
end

for Loop

for file in *.txt
    cp $file $file.bak
end

Functions

Functions in Fish are used to encapsulate commands or create aliases.

function ll
    ls -lhG $argv
end

The code above defines an ll function. Once defined, you can use ll instead of ls -lhG. The $argv variable represents the function's arguments.

function ls
    command ls -hG $argv
end

The code above redefines the ls command. Note the use of command before ls inside the function body to prevent an infinite loop.

Prompt

The fish_prompt function is used to define the command-line prompt.

function fish_prompt
  set_color purple
  date "+%m/%d/%y"
  set_color FF0
  echo (pwd) '>'
  set_color normal
end

After executing the function above, your prompt will look like this:

02/06/13
/home/tutorial > 

Configuration

Fish's configuration file is located at ~/.config/fish/config.fish. It is automatically loaded whenever Fish starts. Fish also provides a web-based interface for configuration.

$ fish_config # Opens the web interface in a browser

Key Features Comparison:

• Running Commands: Compatible with bash-like execution.
• Getting Help: help/man cmd opens in browser/terminal.
• Syntax Highlighting: Real-time command validation.
• Wildcards: Supports recursive matching with **.
• Pipes and Redirections: Use ^ for stderr.
• Autosuggestions: Use Ctrl-f or → to autocomplete.
• Tab Completions: Powerful tab-based completion.
• Variables: Set using set (instead of name=value).
• Exit Status: Use $status instead of $?.
• Exports: Use set -x instead of export.
• Lists: All variables in Fish are actually lists.
• Command Substitutions: Use (cmd) instead of backticks or $().
• Combiners (And, Or, Not): Use words instead of symbols like && or ||.
• Functions: Use $argv instead of $1, $2, etc.
• Conditionals/Loops: Clean, Python-like syntax.
• Startup: Configured via ~/.config/fish/config.fish.
• Universal Variables: Variables shared across all running Fish instances.

Examples:

set name 'czl' # Set a variable
echo $name
echo $status   # Display exit status
env            # List environment variables
set -x MyVar Value # Export a variable
set -e MyVar       # Erase a variable
set PATH $PATH /usr/local/bin # Add to PATH list
set -U fish_user_paths /usr/local/bin $fish_user_paths # Permanent PATH update
touch "testing_"(date +%s)".txt" # Command substitution
cp file.txt file.txt.bak; and echo 'success'; or echo 'fail' # Combiners
functions # List defined functions

References

• Official Fish Shell Website