It can add bindings if given a SEQUENCE of characters to bind to. These should be written as :ref:`fish escape sequences <escapes>`. The most important of these are ``\c`` for the control key, and ``\e`` for escape, and because of historical reasons also the Alt key (sometimes also called "Meta").
For example, :kbd:`Alt`\ +\ :kbd:`W` can be written as ``\ew``, and :kbd:`Control`\ +\ :kbd:`X` (^X) can be written as ``\cx``. Note that Alt-based key bindings are case sensitive and Control-based key bindings are not. This is a constraint of text-based terminals, not ``fish``.
The generic key binding that matches if no other binding does can be set by specifying a ``SEQUENCE`` of the empty string (that is, ``''`` ). For most key bindings, it makes sense to bind this to the ``self-insert`` function (i.e. ``bind '' self-insert``). This will insert any keystrokes not specifically bound to into the editor. Non-printable characters are ignored by the editor, so this will not result in control sequences being inserted.
If the ``-k`` switch is used, the name of a key (such as 'down', 'up' or 'backspace') is used instead of a sequence. The names used are the same as the corresponding curses variables, but without the 'key\_' prefix. (See ``terminfo(5)`` for more information, or use ``bind --key-names`` for a list of all available named keys). Normally this will print an error if the current ``$TERM`` entry doesn't have a given key, unless the ``-s`` switch is given.
``COMMAND`` can be any fish command, but it can also be one of a set of special input functions. These include functions for moving the cursor, operating on the kill-ring, performing tab completion, etc. Use ``bind --function-names`` for a complete list of these input functions.
When ``COMMAND`` is a shellscript command, it is a good practice to put the actual code into a `function <#function>`__ and simply bind to the function name. This way it becomes significantly easier to test the function while editing, and the result is usually more readable as well.
Note that special input functions cannot be combined with ordinary shell script commands. The commands must be entirely a sequence of special input functions (from ``bind -f``) or all shell script commands (i.e., valid fish script).
If no ``SEQUENCE`` is provided, all bindings (or just the bindings in the given ``MODE``) are printed. If ``SEQUENCE`` is provided but no ``COMMAND``, just the binding matching that sequence is printed.
To save custom keybindings, put the ``bind`` statements into :ref:`config.fish <initialization>`. Alternatively, fish also automatically executes a function called ``fish_user_key_bindings`` if it exists.
Key bindings may use "modes", which mimics Vi's modal input behavior. The default mode is "default", and every bind applies to a single mode. The mode can be viewed/changed with the ``$fish_bind_mode`` variable.
-``-e`` or ``--erase`` Erase the binding with the given sequence and mode instead of defining a new one. Multiple sequences can be specified with this flag. Specifying ``-a`` or ``--all`` with ``-M`` or ``--mode`` erases all binds in the given mode regardless of sequence. Specifying ``-a`` or ``--all`` without ``-M`` or ``--mode`` erases all binds in all modes regardless of sequence.
-``--preset`` and ``--user`` specify if bind should operate on user or preset bindings. User bindings take precedence over preset bindings when fish looks up mappings. By default, all ``bind`` invocations work on the "user" level except for listing, which will show both levels. All invocations except for inserting new bindings can operate on both levels at the same time (if both ``--preset`` and ``--user`` are given). ``--preset`` should only be used in full binding sets (like when working on ``fish_vi_key_bindings``).
-``backward-kill-path-component``, move one path component to the left of the cursor to the killring. A path component is everything likely to belong to a path component, i.e. not any of the following: `/={,}'\":@ |;<>&`, plus newlines and tabs.
-``cancel-commandline``, cancel the current commandline and replace it with a new empty one, leaving the old one in place with a marker to show that it was cancelled
-``repaint-mode``, reexecutes the :ref:`fish_mode_prompt <cmd-fish_mode_prompt>` and redraws the prompt. This is useful for vi-mode. If no ``fish_mode_prompt`` exists or it prints nothing, it acts like a normal repaint.
Unix terminals, like the ones fish operates in, are at heart 70s technology. They have some limitations that applications running inside them can't workaround.
For instance, the control key modifies a character by setting the top three bits to 0. This means:
- Many characters + control are indistinguishable from other keys. :kbd:`Control`\ +\ :kbd:`I`*is* tab, :kbd:`Control`\ +\ :kbd:`J`*is* newline (`\n`).
Other keys don't have a direct encoding, and are sent as escape sequences. For example :kbd:`→` (Right) often sends ``\e\[C``. These can differ from terminal to terminal, and the mapping is typically available in `terminfo(5)`. Sometimes however a terminal identifies as e.g. ``xterm-256color`` for compatibility, but then implements xterm's sequences incorrectly.
The escape key can be used standalone, for example, to switch from insertion mode to normal mode when using Vi keybindings. Escape can also be used as a "meta" key, to indicate the start of an escape sequence, like for function or arrow keys. Custom bindings can also be defined that begin with an escape character.
fish waits for a period after receiving the escape character, to determine whether it is standalone or part of an escape sequence. While waiting, additional key presses make the escape key behave as a meta key. If no other key presses come in, it is handled as a standalone escape. The waiting period is set to 30 milliseconds (0.03 seconds). It can be configured by setting the ``fish_escape_delay_ms`` variable to a value between 10 and 5000 ms. This can be a universal variable that you set once from an interactive session.
