fish: Tutorial

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Tutorial

# fish tutorial

# Why fish?

`fish` is a fully-equipped command line shell (like bash or zsh) that is smart and user-friendly. `fish` supports powerful features like syntax highlighting, autosuggestions, and tab completions that just work, with nothing to learn or configure.

If you want to make your command line more productive, more useful, and more fun, without learning a bunch of arcane syntax and configuration options, then `fish` might be just what you're looking for!

# Learning fish

This tutorial assumes a basic understanding of command line shells and Unix commands, and that you have a working copy of `fish`.

If you have a strong understanding of other shells, and want to know what `fish` does differently, search for the magic phrase unlike other shells, which is used to call out important differences.

When you start `fish`, you should see this:

    Welcome to fish, the friendly interactive shell
    Type help for instructions on how to use fish
    you@hostname ~>

`fish` comes with a default prompt that shows your username, hostname, and working directory. You'll see how to change your prompt further down. From now on, we'll pretend your prompt is just a '`>`' to save space.

# Running Commands

`fish` runs commands like other shells: you type a command, followed by its arguments. Spaces are separators:

    > echo hello world
    hello world

You can include a literal space in an argument with a backslash, or by using single or double quotes:

    > mkdir My\ Files
    > cp ~/Some\ File 'My Files'
    > ls "My Files"
    Some File

Commands can be chained with semicolons.

# Getting Help

`fish` has excellent help and man pages. Run `help` to open help in a web browser, and `man` to open it in a man page. You can also ask for help with a specific command, for example, `help set` to open in a web browser, or `man set` to see it in the terminal.

    > man set
    set - handle shell variables
      Synopsis...

# Syntax Highlighting

You'll quickly notice that `fish` performs syntax highlighting as you type. Invalid commands are colored red by default:

    > /bin/mkd

A command may be invalid because it does not exist, or refers to a file that you cannot execute. When the command becomes valid, it is shown in a different color:

    > /bin/mkdir

`fish` will underline valid file paths as you type them:

    > cat ~/somefi

This tells you that there exists a file that starts with '`somefi`', which is useful feedback as you type.

These colors, and many more, can be changed by running `fish_config`, or by modifying variables directly.

# Wildcards

`fish` supports the familiar wildcard `*`. To list all JPEG files:

    > ls *.jpg
    lena.jpg
    meena.jpg
    santa maria.jpg

You can include multiple wildcards:

    > ls l*.p*
    lena.png
    lesson.pdf

Especially powerful is the recursive wildcard ** which searches directories recursively:

    > ls /var/**.log
    /var/log/system.log
    /var/run/sntp.log

If that directory traversal is taking a long time, you can Control-C out of it.

# Pipes and Redirections

You can pipe between commands with the usual vertical bar:

    > echo hello world | wc
           1       2      12

stdin and stdout can be redirected via the familiar < and >. Unlike other shells, stderr is redirected with a caret ^

    > grep fish < /etc/shells > ~/output.txt ^ ~/errors.txt

# Autosuggestions

`fish` suggests commands as you type, and shows the suggestion to the right of the cursor, in gray. For example:

    > /bin/hostname

It knows about paths and options:

    > grep --ignore-case

And history too. Type a command once, and you can re-summon it by just typing a few letters:

    > rsync -avze ssh . myname@somelonghost.com:/some/long/path/doo/dee/doo/dee/doo

To accept the autosuggestion, hit → or Control-F. To accept a single word of the autosuggestion, Alt-→ (right arrow). If the autosuggestion is not what you want, just ignore it.

# Tab Completions

`fish` comes with a rich set of tab completions, that work "out of the box."

Press Tab, and `fish` will attempt to complete the command, argument, or path:

    > /pri @key{Tab} → /private/

If there's more than one possibility, it will list them:

    > ~/stuff/s @key{Tab}
    ~/stuff/script.sh  (Executable, 4.8kB)  ~/stuff/sources/  (Directory)

Hit tab again to cycle through the possibilities.

`fish` can also complete many commands, like git branches:

    > git merge pr @key{Tab} → git merge prompt_designer
    > git checkout b @key{Tab}
    builtin_list_io_merge (Branch) builtin_set_color (Branch) busted_events (Tag)

Try hitting tab and see what `fish` can do!

# Variables

Like other shells, a dollar sign performs variable substitution:

    > echo My home directory is $HOME
    My home directory is /home/tutorial

Variable substitution also occurs in double quotes, but not single quotes:

    > echo "My current directory is $PWD"
    My current directory is /home/tutorial
    > echo 'My current directory is $PWD'
    My current directory is $PWD

Unlike other shells, `fish` has no dedicated syntax for setting variables. Instead it has an ordinary command: `set`, which takes a variable name, and then its value.

    > set name 'Mister Noodle'
    > echo $name
    Mister Noodle

(Notice the quotes: without them, `Mister` and `Noodle` would have been separate arguments, and `$name` would have been made into a list of two elements.)

Unlike other shells, variables are not further split after substitution:

    > mkdir $name
    > ls
    Mister Noodle

In bash, this would have created two directories "Mister" and "Noodle". In `fish`, it created only one: the variable had the value "Mister Noodle", so that is the argument that was passed to `mkdir`, spaces and all. Other shells use the term "arrays", rather than lists.

# Exit Status

Unlike other shells, `fish` stores the exit status of the last command in `$status` instead of `$?`.

    > false
    > echo $status
    1

Zero is considered success, and non-zero is failure.

# Exports (Shell Variables)

Unlike other shells, `fish` does not have an export command. Instead, a variable is exported via an option to `set`, either `--export` or just `-x`.

    > set -x MyVariable SomeValue
    > env | grep MyVariable
    MyVariable=SomeValue

You can erase a variable with `-e` or `--erase`

    > set -e MyVariable
    > env | grep MyVariable
    (no output)

# Lists

The `set` command above used quotes to ensure that `Mister Noodle` was one argument. If it had been two arguments, then `name` would have been a list of length 2. In fact, all variables in `fish` are really lists, that can contain any number of values, or none at all.

Some variables, like `$PWD`, only have one value. By convention, we talk about that variable's value, but we really mean its first (and only) value.

Other variables, like `$PATH`, really do have multiple values. During variable expansion, the variable expands to become multiple arguments:

    > echo $PATH
    /usr/bin /bin /usr/sbin /sbin /usr/local/bin

Lists cannot contain other lists: there is no recursion. A variable is a list of strings, full stop.

Get the length of a list with `count`:

    > count $PATH
    5

You can append (or prepend) to a list by setting the list to itself, with some additional arguments. Here we append /usr/local/bin to $PATH:

    > set PATH $PATH /usr/local/bin

You can access individual elements with square brackets. Indexing starts at 1 from the beginning, and -1 from the end:

    > echo $PATH
    /usr/bin /bin /usr/sbin /sbin /usr/local/bin
    > echo $PATH[1]
    /usr/bin
    > echo $PATH[-1]
    /usr/local/bin

You can also access ranges of elements, known as "slices:"

    > echo $PATH[1..2]
    /usr/bin /bin
    > echo $PATH[-1..2]
    /usr/local/bin /sbin /usr/sbin /bin

You can iterate over a list (or a slice) with a for loop:

    > for val in $PATH
        echo "entry: $val"
      end
    entry: /usr/bin/
    entry: /bin
    entry: /usr/sbin
    entry: /sbin
    entry: /usr/local/bin

Lists adjacent to other lists or strings are expanded as cartesian products unless quoted (see Variable expansion):

    > set -l a 1 2 3
    > set -l 1 a b c
    > echo $a$1
    1a 2a 3a 1b 2b 3b 1c 2c 3c
    > echo $a" banana"
    1 banana 2 banana 3 banana
    > echo "$a banana"
    1 2 3 banana

This is similar to Brace expansion.

# Command Substitutions

Command substitutions use the output of one command as an argument to another. Unlike other shells, `fish` does not use backticks ` for command substitutions. Instead, it uses parentheses:

    > echo In (pwd), running (uname)
    In /home/tutorial, running FreeBSD

A common idiom is to capture the output of a command in a variable:

    > set os (uname)
    > echo $os
    Linux

Command substitutions are not expanded within quotes. Instead, you can temporarily close the quotes, add the command substitution, and reopen them, all in the same argument:

    > touch "testing_"(date +%s)".txt"
    > ls *.txt
    testing_1360099791.txt

# Combiners (And, Or, Not)

Unlike other shells, `fish` does not have special syntax like && or || to combine commands. Instead it has commands `and`, `or`, and `not`.

    > cp file1.txt file1_bak.txt; and echo "Backup successful"; or echo "Backup failed"
    Backup failed

# Conditionals (If, Else, Switch)

Use `if`, `else if`, and `else` to conditionally execute code, based on the exit status of a command.

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

There is also a `switch` command:

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

Note that `case` does not fall through, and can accept multiple arguments or (quoted) wildcards.

# Functions

A `fish` function is a list of commands, which may optionally take arguments. Unlike other shells, arguments are not passed in "numbered variables" like `$1`, but instead in a single list `$argv`. To create a function, use the `function` builtin:

    > function say_hello
         echo Hello $argv
      end
    > say_hello
    Hello
    > say_hello everybody!
    Hello everybody!

Unlike other shells, `fish` does not have aliases or special prompt syntax. Functions take their place.

You can list the names of all functions with the `functions` keyword (note the plural!). `fish` starts out with a number of functions:

    > functions
    alias, cd, delete-or-exit, dirh, dirs, down-or-search, eval, export, fish_command_not_found_setup, fish_config, fish_default_key_bindings, fish_prompt, fish_right_prompt, fish_sigtrap_handler, fish_update_completions, funced, funcsave, grep, help, history, isatty, ls, man, math, nextd, nextd-or-forward-word, open, popd, prevd, prevd-or-backward-word, prompt_pwd, psub, pushd, seq, setenv, trap, type, umask, up-or-search, vared

You can see the source for any function by passing its name to `functions`:

    > functions ls
    function ls --description 'List contents of directory'
        command ls -G $argv
    end

# Loops

While loops:

    > while true
        echo "Loop forever"
    end
    Loop forever
    Loop forever
    Loop forever
    ...

For loops can be used to iterate over a list. For example, a list of files:

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

Iterating over a list of numbers can be done with `seq`:

    > for x in (seq 5)
        touch file_$x.txt
    end

# Prompt

Unlike other shells, there is no prompt variable like PS1. To display your prompt, `fish` executes a function with the name `fish_prompt`, and its output is used as the prompt.

You can define your own prompt:

    > function fish_prompt
        echo "New Prompt % "
    end
    New Prompt %

Multiple lines are OK. Colors can be set via `set_color`, passing it named ANSI colors, or hex RGB values:

    > function fish_prompt
          set_color purple
          date "+%m/%d/%y"
          set_color FF0
          echo (pwd) '>'
          set_color normal
      end
    02/06/13
    /home/tutorial >

You can choose among some sample prompts by running `fish_config prompt`. `fish` also supports RPROMPT through `fish_right_prompt`.

# $PATH

`$PATH` is an environment variable containing the directories in which `fish` searches for commands. Unlike other shells, $PATH is a list, not a colon-delimited string.

To prepend /usr/local/bin and /usr/sbin to `$PATH`, you can write:

    > set PATH /usr/local/bin /usr/sbin $PATH

You can do so directly in `config.fish`, like you might do in other shells with `.profile`. See this example.

A faster way is to modify the `$fish_user_paths` universal variable, which is automatically prepended to `$PATH`. For example, to permanently add `/usr/local/bin` to your `$PATH`, you could write:

    > set -U fish_user_paths /usr/local/bin $fish_user_paths

The advantage is that you don't have to go mucking around in files: just run this once at the command line, and it will affect the current session and all future instances too. (Note: you should NOT add this line to `config.fish`. If you do, the variable will get longer each time you run fish!)

# Startup (Where's .bashrc?)

`fish` starts by executing commands in `~/.config/fish/config.fish`. You can create it if it does not exist.

It is possible to directly create functions and variables in `config.fish` file, using the commands shown above. For example:

    > cat ~/.config/fish/config.fish

    set -x PATH $PATH /sbin/

    function ll
        ls -lh $argv
    end

However, it is more common and efficient to use autoloading functions and universal variables.

# Autoloading Functions

When `fish` encounters a command, it attempts to autoload a function for that command, by looking for a file with the name of that command in `~/.config/fish/functions/`.

For example, if you wanted to have a function `ll`, you would add a text file `ll.fish` to `~/.config/fish/functions`:

    > cat ~/.config/fish/functions/ll.fish
    function ll
        ls -lh $argv
    end

This is the preferred way to define your prompt as well:

    > cat ~/.config/fish/functions/fish_prompt.fish
    function fish_prompt
        echo (pwd) "> "
    end

See the documentation for funced and funcsave for ways to create these files automatically.

# Universal Variables

A universal variable is a variable whose value is shared across all instances of `fish`, now and in the future – even after a reboot. You can make a variable universal with `set -U`:

    > set -U EDITOR vim

Now in another shell:

    > echo $EDITOR
    vim

# Ready for more?

If you want to learn more about fish, there is lots of detailed documentation, an official mailing list, the IRC channel #fish on `irc.oftc.net`, and the github page.