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The Fish Cookbook

From Shell to Plate: Savor the Zest of Fish šŸ¦ž

Welcome to The Fish Cookbook, your ultimate guide to unlocking the full potential of shell scripting with the delightful Fish. With its user-friendliness and convenient features, Fish stands out as a true gem among shells.

Master programming challenges with our curated collection of Fish recipes. Glide through your code with ease, whether you're a seasoned pro or a shell scripting newbie.

This cookbook is licensed under CC BY-NC-SA 4.0, ensuring knowledge and inspiration flow while respecting the rights of others.

What's on the Menu?

Setting Sail

Ahoy there, matey! Prepare to embark on a grand adventure with our trusty mate, Fish. In this section, we'll guide you through the step-by-step setup process to ensure you're ready to navigate the command line seas like a true captain. Let's get your shipshape and ready for the voyage ahead!

How the Shell do I Install Fish?

If you're ready to dive into the wonderful world of Fish, here's how you can get your hands wet. You can either follow the official website for instructions, or stick around and sail through the directions provided here for your OS.

For macOS with Homebrew:

brew update && brew install fish

For Debian:

wget http://download.opensuse.org/repositories/shells:fish:release:2/Debian_8.0/Release.key
apt-key add - < Release.key
echo 'deb http://download.opensuse.org/repositories/shells:/fish:/release:/2/Debian_8.0/ /' >> /etc/apt/sources.list.d/fish.list
apt-get update
apt-get install fish

For Ubuntu:

sudo apt-add-repository ppa:fish-shell/release-2
sudo apt-get update
sudo apt-get install fish

For CentOS:

cd /etc/yum.repos.d/
wget http://download.opensuse.org/repositories/shells:fish:release:2/CentOS_7/shells:fish:release:2.repo
yum install fish

For Fedora:

dnf install fish

For Arch Linux:

pacman -S fish

For Gentoo:

emerge fish

For FreeBSD:

pkg install fish

For NetBSD:

pkgin install fish

For OpenBSD:

pkg_add fish

For the brave who want to build from source:

sudo apt-get -y install git gettext automake autoconf ncurses-dev build-essential libncurses5-dev

git clone -q --depth 1 https://github.com/fish-shell/fish-shell
cd fish-shell
autoreconf && ./configure
make && sudo make install

With Fish installed, a thrilling journey lies ahead. Gear up to explore the command line, unearthing Fish's core treasures and secrets. Here's to abundant and joyous fishing ventures! šŸ»

Making Fish Your Default Shell, Ahoy!

Once you've installed Fish and it's safely located in your $PATH, for example, at /usr/local/bin, you can make it your default shell for a smooth sailing command line experience.

echo /usr/local/bin/fish | sudo tee -a /etc/shells
chsh -s /usr/local/bin/fish

Discovering Fish's Installation Location

Curious about where Fish is installed? Utilize the handy which command.

which fish
/usr/local/bin/fish

Where to Seek Help

If you find yourself in need of assistance or have burning questions about Fish, fret not. There's a treasure trove of resources awaiting you:

Foundations

Decoding Prompts: What Are These Wiggly Characters?

The prompt is where you type commands and interact with Fish. Read more about the UNIX prompt here.

You might encounter something like this:

jb@mbp ~/C/cookbook>

The tilde ~ represents the home directory in a compact form, instead of /users/jb/home, /Users/jb, and so on.

The @ symbol is an arbitrary character chosen to separate the username jb from the computer's name mbp. You can learn to tailor your prompt to display only what's relevant to you.

The forward slash / serves as the path delimiter. At a glance, you can see that the current directory is inside the home directory, under Code/cookbook. The abbreviated path displays just C.

To customize the length of the abbreviated path, use:

set fish_prompt_pwd_dir_length NUMBER

Or, if you prefer not to have abbreviated paths:

set fish_prompt_pwd_dir_length 0

Then, your prompt will look like this:

jb@mbp ~/Code/cookbook>

The greater-than symbol > signifies the end of the prompt.

Not a fan of these conventions? Feel free to craft your own prompt to suit your preferences.

Where Am I in Fish? Discovering Your Current Path

To find your current location in Fish, simply refer to the read-only environment variable $PWD.

echo $PWD
/Users/jb/Code/cookbook

Alternatively, you can use the pwd builtin to determine the current directory.

pwd
/Users/jb/Code/cookbook

In Fish, both $PWD and pwd always resolve symbolic links. This means that if you're inside a directory that's a symbolic reference to another, you'll still get the path to the actual directory.

Interactively, typing pwd is more convenient. For scripting, $PWD is less expensive in terms of function calls.

<details> <summary>Dazzle me!</summary> 
echo "The current working directory is "(pwd)

# Versus

echo "The current working directory is $PWD"
</details>

Searching and Running Commands in Fish: How Do I Do That?

To run a command, type the command's name and press return.

ls

Alternatively, begin typing the command you're looking for and press tab. Fish will use the built-in pager, allowing you to browse and select the command interactively.

Fish determines which commands are available by examining the $PATH environment variable. This variable contains a list of paths, and every binary file inside any of those paths can be run by their name.

Display your $PATH contents with:

printf "%s\n" $PATH
/usr/local/bin
/usr/bin
/bin

To list every command in your system and display them in columns, use:

ls $PATH | column

If the list is truncated, try:

ls $PATH | column | less

Navigate the list using k and j to move down/up, and press q to exit.

The $PATH variable is created at the beginning of the Fish process during environment initialization. You can modify, prepend, or append this variable yourself, for example, in ~/.config/fish/config.fish.

In addition to the type, builtin, and functions built-ins mentioned earlier, *nix systems often include one or more shell-agnostic alternatives such as which, apropos, whatis, and others.

These commands have overlapping functionality but also possess unique features. Consult your system's manpage for more information.

Did My Command Succeed in Fish?

Every command returns an exit code to indicate whether it succeeded or not. An exit code of 0 means success, while any other value signifies failure. Different commands use various integers to represent possible errors.

In Fish, you can check the exit code of any command using the read-only variable $status.

my_command
echo $status

When working with pipes, Fish provides a helpful variable called $pipestatus that allows you to check the exit codes of all commands in a pipeline.

Suppose you have a pipeline like this:

command1 | command2 | command3

To find the exit codes of all commands in the pipeline, use $pipestatus:

echo $pipestatus

This will print an array of exit codes, one for each command in the pipeline. For example, if command1 succeeded, command2 failed with an exit code of 2, and command3 failed with an exit code of 1, the output would look like this:

0 2 1

With $pipestatus, you can conveniently keep an eye on the success and failure of commands in your pipelines.

What's the Fish Shebang All About? Making Scripts Executable

The shebang is a special comment that instructs the shell to run a script using a specific program, such as node or python.

To run a script with fish by default, add a shebang to the first line of your file:

#!/usr/bin/env fish
<details> <summary>Give me the scoop!</summary> 
#!/usr/bin/env fish

echo "Check this out, ma'! I'm a Fish on wheels šŸ›¼"

Save that to a file and mark it as executable.

chmod +x my_script

The system above allows you to run the script directly by using its path:

./my_script

instead of:

fish my_script
</details>

How Do I Debug My Fish Scripts Interactively? Navigating with Breakpoints

To interactively debug your Fish scripts, use the breakpoint builtin. Simply drop it anywhere in your script where you want to pause execution and launch an interactive debugging prompt.

function some_function
    set --local files (ls ~)
    breakpoint # when this is executed, an interactive prompt will be launched and you will be able to inspect $files
    # ... rest of function is not executed until you exit from debugger
end

With breakpoint, you can take a closer look at your script's execution, inspect variables, and navigate through the script.

Where to find Fish's equivalent of .bash_profile or .bashrc?

In Fish shell, your configuration is stored in the config.fish file located at ~/.config/fish/config.fish. This file serves as Fish's equivalent to .bash_profile or .bashrc in Bash. It allows you to customize and configure your Fish shell environment by adding functions, environment variables, and other personalized settings.

All About Variables

How Do I Set Variables in Fish? A Quick Guide to Variable Scopes

To set variables in Fish, use the set builtin.

set foo 42

The set builtin accepts the following flags to explicitly declare the scope of the variable:

If no scope modifier is used, the variable will be local to the current function; otherwise, it will be global.

If the variable has already been defined, the previous scope will be used.

Local Variables

The variable foo will not be available outside of the if block.

if true
    set -l foo 42
end

echo "foo=$foo" # foo=

Global Variables

The variable foo will be available outside the if block.

if true
    set -g foo 42
end

echo "foo=$foo" # foo=42

Universal Variables

The variable foo will be preserved and available to future shell sessions.

set -U foo 42
fish
echo "foo=$foo" # foo=42

Exported Variables

The variable foo will be local and exported, therefore available to the fish child process created inside the if block.

if true
    set -lx foo 42
    fish -c 'echo "foo=$foo"' # foo=42
end

The variable foo will be global, but since it's not exported, it won't be available to the fish child process.

set -g foo 42
fish -c 'echo "foo=$foo"' # foo=

The variable GPG_AGENT_INFO will be universal and exported, therefore preserved across future shell sessions and child processes.

set -Ux GPG_AGENT_INFO /Users/jb/.gnupg/S.gpg-agent:12345:2

Now you're set to sail through the variable seas of Fish!

How Do I Export a Variable in Fish?

To export a variable in Fish, use the set builtin along with the scope modifier -x or --export.

set -x foo 42
fish -c 'echo "foo=$foo"' # foo=42

By using the -x or --export option, you're ensuring that the variable is available to any child process spawned in the current session.

How Do I List All Environment Variables in Fish?

To list all environment variables in Fish, use the set builtin without any modifier flags.

set

If you prefer to see only the variable names without the values, employ the --names option:

set --names

And for a full view of each variable without truncating long lines, go with --long:

set --long

How Do I Set the $PATH Persistently in Fish?

To persistently add a path to your $PATH in Fish, make use of the $fish_user_paths variable.

set -U fish_user_paths $fish_user_paths my_path

If you're using Fish 3.2.1 or later, you can opt for the built-in fish_add_path function instead.

fish_add_path my_path

See $PATH in the Fish tutorial for juicy information.

How Do I Remove a Path from the $PATH in Fish?

To remove a path from the $PATH in Fish, use the set builtin with the -e or --erase flag, combined with the contains builtin to find the index of the path you'd like to remove.

if set -l index (contains -i $my_path $PATH)
    set -e PATH[$index]
end

How Do I Remove a Path Persistently from the $PATH in Fish?

To remove a path persistently from the $PATH in Fish, use the set builtin with the -e or --erase flag, combined with the contains builtin to find the index of the path you'd like to remove from the $fish_user_paths variable.

if set -l index (contains -i $my_path $fish_user_paths)
    set -e -U fish_user_paths[$index]
end

How Do I Check if a Path Exists in the $PATH in Fish?

To check if a path exists in the $PATH in Fish, use the contains builtin. This handy tool helps you verify whether your desired path is swimming along with the other paths in your $PATH variable. šŸ 

if contains $my_path $PATH
    # $my_path is in $PATH
end

All About Functions

How Do I Whip Up a Function in Fish?

Crafting a function in Fish is a piece of cake! Just use the function builtin to start creating your shell masterpiece.

function mkdirp
    mkdir -p $argv
end

To make sure this function stays fresh in future Fish sessions, save it to ~/.config/fish/functions/mkdirp.fish. A neat way to accomplish this is by using the funcsave function.

funcsave mkdirp

Alternatively, you can use the functions builtin to write the function definition to a file, like a secret recipe for your custom shell commands.

functions mkdirp > ~/.config/fish/functions/mkdirp.fish

How Do I Craft a "Private" Function in Fish?

While Fish doesn't have built-in private functions, you can still be sneaky! Use a custom namespace to prefix any function you want to treat as private.

function _prefix_my_function
end

You can also simulate private scope using functions -e.

<details> <summary>Show me the secret sauce!</summary> 
function foo
    function _foo
        echo Foo
        functions -e _foo # Erase _foo
    end
    _foo
end
</details>

This workaround helps you keep some Fish functions under wraps, like a top-secret ingredient in your shell recipe.

Should Function Names and File Names Be a Perfect Match?

Absolutely! Fish's lazy-loading / autoloading mechanism depends on this match made in heaven.

If you have a file ~/.config/fish/functions/foo.fish with a valid function definition bar:

  1. In a new shell, trying to run bar produces an unknown-command error.
  2. Typing foo will highlight as a valid command, but produce an unknown-command error.
  3. Trying to run bar again now works like a charm.
<details> <summary>Show me the magic!</summary>

Save bar to ~/.config/fish/functions/foo.fish.

function bar
    echo Bar
end
functions bar > ~/.config/fish/functions/foo.fish

Create a new shell session.

fish

Try to run bar, then foo, then bar again.

bar
# fish: Unknown command 'bar'
foo
# fish: Unknown command 'foo'
bar
# Bar
</details>

Can I Fit Multiple Functions in a Single File?

Yes, indeed! You can define as many functions as you want in a single file. Just remember that Fish doesn't have private functions, so every function in the file will end up in the global scope when the file is loaded.

Since functions are eagerly loaded, defining multiple functions in a single file might not be as efficient as the one-function-per-file approach, which leverages Fish's autoloading capabilities. So, while it's possible to have multiple functions in one file, spreading them across separate files might give you a performance boost and a more organized structure.

How Do I Reveal a Function's Definition in Fish?

If you're certain that the command you're looking for is a function, you can use the functions builtin to display its definition:

functions my_function

On the other hand, if you're not sure whether the command is a function, a builtin, or a system command, you can rely on the type command to reveal its true nature:

type my_function
my_function is a function with definition
# ... function definition ...

Using type, you can easily identify what kind of command you're dealing with and get the information you need.

Exploring Functions, Builtins, and Commands in Fish

In Fish, commands, functions, and builtins each serve different purposes and are defined in different ways:

These different types of commands help make Fish a versatile and powerful shell, allowing for a wide range of customization and utility.

Displaying the Fish Function Roster

To list all the functions defined in Fish, employ the functions builtin without any arguments. Note that hidden functionsā€”those with names starting with an underscoreā€”won't be displayed. To reveal everything, including hidden functions, use functions -a or functions --all.

For a different approach, launch the Fish web-based configuration and head to the /functions tab by running:

fish_config functions

Verifying a Function's Existence in Fish

The type function is your go-to tool for checking whether a function exists in Fish. It provides information about commands, builtins, or functions.

if not type --quiet "$command_name"
    exit 1
end
<details> <summary>For builtins, use <code><a href="https://fishshell.com/docs/current/cmds/builtin.html">builtin --names</a></code>.</summary> 
if not contains -- "$command_name" (builtin --names)
    exit 1
end
</details> <details> <summary>For functions, employ <code><a href="https://fishshell.com/docs/current/cmds/functions.html">functions --query</a></code>.</summary> 
if not functions --query "$command_name"
    exit 1
end
</details> <details> <summary>For other commands, utilize <code><a href="https://fishshell.com/docs/current/cmds/command.html">command --search</a></code>.</summary> 
if not command --search "$command_name" > /dev/null
    exit 1
end

In Fish >= 2.5, it's even easier:

if not command --search --quiet "$command_name"
    exit 1
end
</details>

All About Arguments

Accessing Function Arguments in Fish

To access the arguments passed to a function in Fish, simply use the $argv variable.

function Foo
    printf "%s\n" $argv
end

Foo foo bar baz
foo
bar
baz

Accessing Script Arguments in Fish

To access the arguments passed to a script in Fish, use $argv.

fish ./my_script foo bar baz
foo
bar
baz
<details> <summary>Example: my_script</summary> 
#!/usr/bin/env fish
printf "%s\n" $argv
</details>

Parsing Command Line Arguments in Fish

To parse command line arguments in Fish, you can use a for loop.

for option in $argv
    switch "$option"
        case -f --foo
        case -b --bar
        case \*
            printf "error: Unknown option %s\n" $option
    end
end

For a more powerful parsing solution, you can explore Fish's official argparse builtin. Another option is to consider using getopts, which is a different approach to CLI parsing.

All About Aliases

The Art of Defining Aliases in Fish

Fish offers the alias function to create a convenient alias:

alias rimraf "rm -rf"

This creates a function like:

function rimraf --wraps='rm -rf' --description 'alias rimraf rm -rf'
  rm -rf $argv;
end

Be aware that aliases created with alias won't be available in new shell sessions. To make them persistent, use:

alias -s ...

This saves the alias to ~/.config/fish/functions/[alias-name].fish

The Problem with Aliases in config.fish

Defining aliases inside ~/.config/fish/config.fish slows down your shell start since each alias/function is eagerly loaded.

To persist aliases across shell sessions, use alias -s, which creates a function and saves it to ~/.config/fish/functions. This leverages Fish function lazy-loading / autoloading mechanism.

IO

Reading a File with Fish

To gracefully read a file line by line in Fish, employ the read builtin.

while read -la line
    echo $line
end < my_file

Reading from stdin and Redirecting Like a Pro in Fish

To read from stdin in Fish, the read builtin is your best friend.

read --prompt "echo 'Name: ' " -l name

Name: Flipper

echo $name
Flipper

To read from an arbitrary input stream, combine read with the while builtin.

while read -la line
    echo $line
end

Mastering Redirection in Fish

To redirect stderr to $my_file:

my_command 2> $my_file

To redirect stdout to $my_file:

my_command > $my_file

To redirect stdout to stderr:

my_command >&2

To redirect stderr to stdout:

my_command 2>&1

Concurrency: Making Your Fish Swim Faster

Run Commands in the Background with Fish

To run a command in the background in Fish, simply use &.

sleep 10 &

Checking Background Jobs in Fish

To see if background jobs are running in Fish, use the jobs builtin.

if jobs > /dev/null
    echo Busy
end

Synchronize Background Tasks in Fish Like a Pro

Fish 3.0.0 introduced a dedicated wait builtin for easy synchronization of background tasks. But if you're curious about how it was done before wait existed, here's a throwback recipe for you.

First, to check if tasks are running in the background, parse the output from the jobs builtin.

<details> <summary>Parse by Job ID</summary> 
function get_jobs
    jobs $argv | command awk -v FS=\t '
        /[0-9]+\t/{
            jobs[++nJobs] = $1
        }
        END {
            for (i in jobs) {
                print(jobs[i])
            }
            exit nJobs == 0
        }
    '
end
</details> <details> <summary>Parse by Group ID</summary> 
function get_jobs
    jobs -g | command awk 'NR > 0 { print; i++ } END { exit i == 0 }'
end
</details>

Next, block the foreground until all background jobs are finished.

function wait
    while true
        set -l has_jobs
        set -l all_jobs (get_jobs)
        or break

        for j in $argv
            if contains -- $j $all_jobs
                set -e has_jobs
                break
            end
        end

        if set -q has_jobs
            break
        end
    end
end

Here's an example of our code in action.

set -l urls "https://"{google,twitter,youtube,facebook,github}".com"

for url in $urls
    fish -c "curl -Lw \"$url: %{time_total}s\n\" -o /dev/null -s $url" &
end

wait (get_jobs)

Glossary

Here is a concise glossary of key terms and concepts mentioned in the Fish Shell Cookbook:

These terms provide a high-level understanding of the key concepts covered in the Fish Cookbook. Refer to the respective sections in this document for more detailed information and practical examples.

Contributing

Ahoy there! We're excited to have you on board for the Fish Cookbook adventure! Your contributions can make this Cookbook a valuable resource for the Fish Shell community. So, let's dive in and follow the guidelines below.

You can contribute to the Cookbook in a few ways:

To join our crew and contribute to the Cookbook, follow these guidelines:

  1. Set your sails and fork the repository. Then, create a new branch for your contributionsā€”a safe space for your changes.
  2. Work your magic in the new branch. Ensure that the content is accurate, clear, and follows the agreed-upon structure. We're all on the same ship here!
  3. If you're adding a new recipe, choose a catchy and informative titleā€”one that grabs attention!
  4. Commit your changes and write a descriptive commit message to let us know what your changes are all about. Be as detailed as a well-crafted map!
  5. Push your branch to your forked repository, like a captain charting new waters.
  6. Open a pull request against the main repository. Share the story behind your changes and why they're valuable. The more we know, the better we can appreciate your work!

Once your pull request is submitted, our trusty crew of maintainers will review it. They may provide feedback or request some tweaks before we hoist the flag and merge your contribution.

You have our heartfelt gratitude for lending a hand in enhancing the Fish Cookbook. We value your efforts, and together, we'll create a fantastic resource for the Fish community. Ahoy!

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