Use ``set -q var``. For example, ``if set -q var; echo variable defined; end``. To check multiple variables you can combine with ``and`` and ``or`` like so::
if set -q var1; or set -q var2
echo either variable defined
end
Keep in mind that a defined variabled could be empty. Both of these commands define an empty variable: ``set var`` and ``set var ""``.
How do I check whether a variable is not empty?
-----------------------------------------------
Use ``string length -q -- $var``. For example, ``if string length -q -- $var; echo not empty; end``. Note that ``string length`` will interpret a list of multiple variables as a disjunction (meaning any/or)::
if string length -q -- $var1 $var2 $var3
echo at least one of these variables is not empty
end
Alternatively, use ``test -n "$var"``, but remember that **the variable must be double-quoted**. For example, ``if test -n "$var"; echo not empty; end``. The ``test`` command provides its own and (-a) and or (-o)::
Use the web configuration tool, :ref:`fish_config <cmd-fish_config>`, or alter the `fish_color family of environment variables <index#variables-color>`__.
If fish is unable to locate a command with a given name, and it starts with '``.``', '``/``' or '``~``', fish will test if a directory of that name exists. If it does, it is implicitly assumed that you want to change working directory. For example, the fastest way to switch to your home directory is to simply press ``~`` and enter.
The ``open`` command uses the MIME type database and the ``.desktop`` files used by Gnome and KDE to identify filetypes and default actions. If at least one of these environments is installed, but the open command is not working, this probably means that the relevant files are installed in a non-standard location. Consider `asking for more help <index#more-help>`__.
If you installed fish manually (e.g. by compiling it, not by using a package manager), you first need to add fish to the list of shells by executing the following command (assuming you installed fish in /usr/local)::
echo /usr/local/bin/fish | sudo tee -a /etc/shells
If you installed a prepackaged version of fish, the package manager should have already done this for you.
In order to change your default shell, type::
chsh -s /usr/local/bin/fish
You may need to adjust the above path to e.g. ``/usr/bin/fish``. Use the command ``which fish`` if you are unsure of where fish is installed.
Unfortunately, there is no way to make the changes take effect at once. You will need to log out and back in again.
I'm seeing weird output before each prompt when using screen. What's wrong?
Fish is trying to set the titlebar message of your terminal. While screen itself supports this feature, your terminal does not. Unfortunately, when the underlying terminal doesn't support setting the titlebar, screen simply passes through the escape codes and text to the underlying terminal instead of ignoring them. It is impossible to detect and resolve this problem from inside fish since fish has no way of knowing what the underlying terminal type is. For now, the only way to fix this is to unset the titlebar message, as suggested above.
Note that fish has a default titlebar message, which will be used if the fish_title function is undefined. So simply unsetting the fish_title function will not work.
How do I change the greeting message?
-------------------------------------
Change the value of the variable ``fish_greeting`` or create a ``fish_greeting`` function. For example, to remove the greeting use::
set fish_greeting
Why doesn't history substitution ("!$" etc.) work?
Because history substitution is an awkward interface that was invented before interactive line editing was even possible. Fish drops it in favor of perfecting the interactive history recall interface. Switching requires a small change of habits: if you want to modify an old line/word, first recall it, then edit. E.g. don't type "sudo !!" - first press Up, then Home, then type "sudo ".
- As in any modern shell, the Up arrow, :kbd:`↑` recalls whole lines, starting from the last line executed. A single press replaces "!!", later presses replace "!-3" and the like.
- If the line you want is far back in the history, type any part of the line and then press Up one or more times. This will constrain the recall to lines that include this text, and you will get to the line you want much faster. This replaces "!vi", "!?bar.c" and the like.
-:kbd:`Alt+↑,Up` recalls individual arguments, starting from the last argument in the last line executed. A single press replaces "!$", later presses replace "!!:4" and the like.
- If the argument you want is far back in history (e.g. 2 lines back - that's a lot of words!), type any part of it and then press :kbd:`Alt+↑,Up`. This will show only arguments containing that part and you will get what you want much faster. Try it out, this is very convenient!
- If you want to reuse several arguments from the same line ("!!:3*" and the like), consider recalling the whole line and removing what you don't need (:kbd:`Alt+D` and :kbd:`Alt+Backspace` are your friends).
In fish versions prior to 2.5.0 it was possible to create a function named ``-`` that would do ``cd -``. Changes in the 2.5.0 release included several bug fixes that enforce the rule that a bare hyphen is not a valid function (or variable) name. However, you can achieve the same effect via an abbreviation::
Fish reserves the `Unicode private-use character range <http://www.unicode.org/faq/private_use.html>`__ from U+F600 thru U+F73F for internal use. Any attempt to feed characters in that range to fish will result in them being replaced by the Unicode "replacement character" U+FFFD. This includes both interactive input as well as any file read by fish (but not programs run by fish).
The fish user community extends fish in unique and useful ways via scripts that aren't always appropriate for bundling with the fish package. Typically because they solve a niche problem unlikely to appeal to a broad audience. You can find those extensions, including prompts, themes and useful functions, in various third-party repositories. These include:
