A shell is a program that helps you operate your computer by starting other programs. fish offers a command-line interface focused on usability and interactive use.
-**Extensive UI**: :ref:`Syntax highlighting <color>`, :ref:`autosuggestions`, :ref:`tab completion <tab-completion>` and selection lists that can be navigated and filtered.
If you are already familiar with other shells like bash and want to see the scripting differences, see :ref:`Fish For Bash Users <fish_for_bash_users>`.
The simplest method is to set your terminal emulator (eg GNOME Terminal, Apple's Terminal.app, or Konsole) to start fish directly. See its configuration and set the program to start to ``/usr/local/bin/fish`` (if that's where fish is installed - substitute another location as appropriate).
Alternatively, you can set fish as your login shell so that it will be started by all terminal logins, including SSH.
..warning::
Setting fish as your login shell may cause issues, such as an incorrect :envvar:`PATH`. Some operating systems, including a number of Linux distributions, require the login shell to be Bourne-compatible and to read configuration from ``/etc/profile``. fish may not be suitable as a login shell on these systems.
Again, substitute the path to fish for ``/usr/local/bin/fish`` - see ``command -s fish`` inside fish. To change it back to another shell, just substitute ``/usr/local/bin/fish`` with ``/bin/bash``, ``/bin/tcsh`` or ``/bin/zsh`` as appropriate in the steps above.
Because shell scripts are written in many different languages, they need to carry information about which interpreter should be used to execute them. For this, they are expected to have a first line, the shebang line, which names the interpreter executable.
For a script written in another language, just replace ``/bin/bash`` with the interpreter for that language. For example: ``/usr/bin/python`` for a python script, or ``/usr/local/bin/fish`` for a fish script, if that is where you have them installed.
If you want to share your script with others, you might want to use :command:`env` to allow for the interpreter to be installed in other locations. For example::
This will call ``env``, which then goes through :envvar:`PATH` to find a program called "fish". This makes it work, whether fish is installed in /usr/local/bin/fish or /usr/bin/fish or ~/.local/bin/fish, as long as that directory is in :envvar:`PATH`.
The shebang line is only used when scripts are executed without specifying the interpreter. For functions inside fish or when executing a script with ``fish /path/to/script``, a shebang is not required (but it doesn't hurt!).
When executing files without an interpreter, fish, like other shells, tries your system shell, typically /bin/sh. This is needed because some scripts are shipped without a shebang line.
These files are read on the startup of every shell, whether interactive and/or if they're login shells. Use ``status --is-interactive`` and ``status --is-login`` to do things only in interactive/login shells, respectively.
This is the short version; for a full explanation, like for sysadmins or integration for developers of other software, see :ref:`Configuration files <configuration>`.
This is just an example; using :doc:`fish_add_path <cmds/fish_add_path>` e.g. ``fish_add_path ~/linux/bin`` which only adds the path if it isn't included yet is easier.
