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!
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.
This runs the command ``echo`` with the arguments ``hello`` and ``world``. In this case that's the same as one argument ``hello world``, but in many cases it's not. If you need to pass an argument that includes a space, you can :ref:`escape <escapes>` with a backslash, or :ref:`quote <quotes>` it using single or double quotes::
Run ``help`` to open fish's help in a web browser, and ``man`` with the page (like ``fish-language``) 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.
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::
To accept the autosuggestion, hit :kbd:`→` (right arrow) or :kbd:`Control`\ +\ :kbd:`F`. To accept a single word of the autosuggestion, :kbd:`Alt`\ +\ :kbd:`→` (right arrow). If the autosuggestion is not what you want, just ignore it.
Unlike other shells, fish has no dedicated ``VARIABLE=VALUE`` syntax for setting variables. Instead it has an ordinary command: ``set``, which takes a variable name, and then its value.
(Notice the quotes: without them, ``Mister`` and ``Noodle`` would have been separate arguments, and ``$name`` would have been made into a list of two elements.)
Unlike other shells, variables are not further split after substitution::
In bash, this would have created two directories "Mister" and "Noodle". In fish, it created only one: the variable had the value "Mister Noodle", so that is the argument that was passed to ``mkdir``, spaces and all. Other shells use the term "arrays", rather than lists.
Sometimes you need to have a variable available to an external command, often as a setting. For example many programs like ``git`` or ``man`` read the ``$PAGER`` variable to figure out your preferred pager (the program that lets you scroll text). Other variables used like this include ``$BROWSER``, ``$LANG`` (to configure your language) and ``$PATH``. You'll note these are written in ALLCAPS, but that's just a convention.
To give a variable to an external command, it needs to be "exported". Unlike other shells, fish does not have an export command. Instead, a variable is exported via an option to ``set``, either ``--export`` or just ``-x``.
This works the other way around as well! If fish is started by something else, it inherits that parents exported variables. So if your terminal emulator starts fish, and it exports ``$LANG`` set to ``en_US.UTF-8``, fish will receive that setting. And whatever started your terminal emulator also gave *it* some variables that it will then pass on unless it specifically decides not to. This is how fish usually receives the values for things like ``$LANG``, ``$PATH`` and ``$TERM``, without you having to specify them again.
Exported variables can be local or global or universal - "exported" is not a :ref:`scope <variables-scope>`! Usually you'd make them global via ``set -gx MyVariable SomeValue``.
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.
Variables whose name ends in "PATH" are automatically split on colons to become lists. They are joined using colons when exported to subcommands. This is for compatibility with other tools, which expect $PATH to use colons. You can also explicitly add this quirk to a variable with ``set --path``, or remove it with ``set --unpath``.
Lists adjacent to other lists or strings are expanded as :ref:`cartesian products <cartesian-product>` unless quoted (see :ref:`Variable expansion <expand-variable>`)::
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::
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::
Unlike other shells, fish does not split command substitutions on any whitespace (like spaces or tabs), only newlines. This can be an issue with commands like ``pkg-config`` that print what is meant to be multiple arguments on a single line. To split it on spaces too, use ``string split``.
This indicates how the command fared - 0 usually means success, while the others signify kinds of failure. For instance fish's ``set --query`` returns the number of variables it queried that weren't set - ``set --query PATH`` usually returns 0, ``set --query arglbargl boogagoogoo`` usually returns 2.
Here, ``make`` is only executed if ``./configure`` succeeds (returns 0), and ``sudo make install`` is only executed if both ``./configure`` and ``make`` succeed.
fish also supports :ref:`and <cmd-and>`, :ref:`or <cmd-or>`, and :ref:`not <cmd-not>`. The first two are job modifiers and have lower precedence. Example usage::
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 :ref:`function <cmd-function>` builtin::
You can list the names of all functions with the :ref:`functions <cmd-functions>` builtin (note the plural!). fish starts out with a number of functions::
Unlike other shells, there is no prompt variable like ``PS1``. To display your prompt, fish executes the :ref:`fish_prompt <cmd-fish_prompt>` function and uses its output as the prompt. And if it exists, fish also executes the :ref:`fish_right_prompt <cmd-fish_right_prompt>` function and uses its output as the right prompt.
Then, if you are happy with it, you can save it to disk by typing ``funcsave fish_prompt``. This saves the prompt in ``~/.config/fish/functions/fish_prompt.fish``. (Or, if you want, you can create that file manually from the start.)
Multiple lines are OK. Colors can be set via :ref:`set_color <cmd-set_color>`, passing it named ANSI colors, or hex RGB values::
``$PATH`` is an environment variable containing the directories that fish searches for commands. Unlike other shells, $PATH is a :ref:`list <tut-lists>`, not a colon-delimited string.
Fish takes care to set ``$PATH`` to a default, but typically it is just inherited from fish's parent process and is set to a value that makes sense for the system - see :ref:`Exports <tut-exports>`.
For compatibility with other shells and external commands, $PATH is a :ref:`path variable<variables-path>`, and so will be joined with colons (not spaces) when you quote it::
A faster way is to use the :ref:`fish_add_path <cmd-fish_add_path>` function, which adds given directories to the path if they aren't already included. It does this by modifying the ``$fish_user_paths``:ref:`universal variable <tut-universal>`, which is automatically prepended to ``$PATH``. For example, to permanently add ``/usr/local/bin`` to your ``$PATH``, you could write::
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. You can also add this line to :ref:`config.fish <tut-config>`, as it only adds the component if necessary.
Or you can modify $fish_user_paths yourself, but you should be careful *not* to append to it unconditionally in config.fish, or it will grow longer and longer.
If you want to organize your configuration, fish also reads commands in .fish files in ``~/.config/fish/conf.d/``. See :ref:`Configuration Files <configuration>` for the details.
When fish encounters a command, it attempts to autoload a function for that command, by looking for a file with the name of that command in ``~/.config/fish/functions/``.
See the documentation for :ref:`funced <cmd-funced>` and :ref:`funcsave <cmd-funcsave>` for ways to create these files automatically, and :ref:`$fish_function_path <syntax-function-autoloading>` to control their location.
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``::
This assumes you installed fish to /usr/local/bin, which is the default location when you've compiled it yourself. If you installed it with a package manager, the usual location is /usr/bin/fish, but package managers typically already add it to /etc/shells. Just substitute the correct location.
If you want to learn more about fish, there is :ref:`lots of detailed documentation <intro>`, the `official gitter channel <https://gitter.im/fish-shell/fish-shell>`__, an `official mailing list <https://lists.sourceforge.net/lists/listinfo/fish-users>`__, and the `github page <https://github.com/fish-shell/fish-shell/>`__.