============
Bash Aliases
============

Intro
-----

Read the `bash docs on aliases`_. Basically, we do something like
this:

.. _`bash docs on aliases`:
   https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Aliases

.. code-block:: bash

   alias ls='ls --classify --color=auto'
   alias tt='tree -CFa'

Then, when we run the “command” ``ls``, it will actually run
``ls --classify --color=auto`` and when we run ``tt`` it will actually
run ``tree -CFa``

How To Unalias‽
---------------

We *aliased* ``ls`` to ``ls``. It is not uncommon to do this for some
commands. But what if we want to run the “original” ``ls``, not its
aliased version? What if we don't want ``--classify`` or
``--color=auto`` in a given situation? Then we can make prevent the
shell from treating the word as an alias to be expanded.

The bash man page on the Aliases section states that:

   "The first word of each simple command, if unquoted, is checked to
   see if it has an alias. If so, that word is replaced by the text of
   the alias."

   \-\- Bash man page on the Aliases section

According to the man page, if we quote the word, bash won't try to
treat it as an alias to be expanded.

How do we do this *quoting* thing‽ We can use either single or double
quotation marks or escape it with a basckslash.

.. figure:: ./bash-aliases.assets/2021-09-08-08-03-03.png
   :alt: ls command aliased and unaliased runs

The screenshot shows how to see what an alias expands to (``alias
ls``) and then proceeds to first run the aliased ``ls``, which shows
classification indication (“/” at the end of directories, “*” at the
end of executable files, etc. and different colors for different types
of files as well, like bluish for directories and greenish for
executables). Then, the remaining three commands show the ways to
quote a *word*.

.. NOTE::

   In bash, in certain contexts the basckslash **is not** an escape,
   but a quoting mechanism.

Manually Expanding Aliases
--------------------------

When the word at the cursor is an alias, we can expand it. For
example, type ``ls``:kbd:`Esc`:kbd:`Tab`. `Esc` can also be triggered
with :kbd:`Ctrl-[`.

.. code:: shell-session

   $ alias ls='ls --classify --color=always'
   $ ls<Esc><Tab>

The line gets replaced with:

.. code:: shell-session

   $ ls --classify --color=always




Tricky aliases 😮
-----------------

One could be evil and create an alias with this:

.. code:: bash

   alias '\ls'='ls ...'

Then one would try to prevent the ``ls`` alias with ``\ls`` but that
would be itself an alias... Thankfully, as of 2021 (at least), Bash
doesn't allow aliases name like that.

Another example:

.. code:: shell-session

   $ 'he'
   -bash: he: command not found

   $ alias w00t='echo w00t'

   $ w00t
   w00t

   $ \w00t
   -bash: w00t: command not found

   $ 'w00t'
   -bash: w00t: command not found