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>`.
There are multiple ways to switch to fish (or any other shell) as your default.
The simpler is to set your terminal to start fish. 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).
The more involved and complete way is to set fish as your login shell. To do that, you need to:
1. Add the shell to ``/etc/shells`` with::
> echo /usr/local/bin/fish | sudo tee -a /etc/shells
2. Change your default shell with::
> chsh -s /usr/local/bin/fish
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.
Setting fish as your login shell may have issues, because some operating systems (including a bunch of linux distributions) only do some of their configuration in shell startup files like /etc/profile. So you could notice e.g. $PATH being wrong, and you would have to redo that setup.
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).
This line is only needed 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!).
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 :ref:`fish_add_path <cmd-fish_add_path>` e.g. ``fish_add_path ~/linux/bin`` which only adds the path if it isn't included yet is easier.
