``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!
Getting started
---------------
Once installed, just type in ``fish`` into your current shell to try it out!
You will be greeted by the standard fish prompt,
which means you are all set up and can start using 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.
``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.
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 `$PATH`. You'll note these are written in ALLCAPS, but that's just a convention.
To give a variable to an external command, it needs to be "exported". Unlike other shells, ``fish`` does not have an export command. Instead, a variable is exported via an option to ``set``, either ``--export`` or just ``-x``.
The ``set`` command above used quotes to ensure that ``Mister Noodle`` was one argument. If it had been two arguments, then ``name`` would have been a list of length 2. In fact, all variables in ``fish`` are really lists, that can contain any number of values, or none at all.
Some variables, like ``$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::
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.
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::
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.
``$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.
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 $fish_user_paths yourself, but you should be careful *not* to append to it unconditionally in config.fish, or it will grow longer and longer.
If you want to organize your configuration, fish also reads commands in .fish files in ``~/.config/fish/conf.d/``. See :ref:`initialization <initialization>` for the details.
When ``fish`` encounters a command, it attempts to autoload a function for that command, by looking for a file with the name of that command in ``~/.config/fish/functions/``.
For example, if you wanted to have a function ``ll``, you would add a text file ``ll.fish`` to ``~/.config/fish/functions``::
See the documentation for :ref:`funced <cmd-funced>` and :ref:`funcsave <cmd-funcsave>` for ways to create these files automatically, and :ref:`$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``::
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/>`__.