This file: http://user.it.uu.se/~embe8573/tty-emacs-keys.txt
           https://dataswamp.org/~incal/tty-emacs-keys.txt


The Linux console: special shortcuts in Emacs
---------------------------------------------

This tutorial describes how to get special
shortcuts (e.g., C-0) in an Emacs instance that
runs in a tty.

This Linux console/VT/tty solution works on
Debian, and probably on many other distros as
well, with only minor or none modifications
required. (VT = Virtual Terminal, tty =
teletypewriter, console = console - all the
same at least with respect to this tutorial.)

If you are inpatient, you can deduct how it is
done from these two configuration files -

    * console remap:
        http://user.it.uu.se/~embe8573/conf/remap.inc

    * Emacs bindings:
        http://user.it.uu.se/~embe8573/conf/emacs-init/console-keys.el

- otherwise the below tutorial describes how
the get the C-0 shortcut working.

In the file

    /etc/console-setup/remap.inc

type

    control keycode 11 = U+0110

Obviously, 'control' is the "Ctrl" key, or C-
in Emacs notation. (There is also "alt" and
"shift", and they can be combined.)

'11' is the keycode for the key '0' in the
console, which you learn from invoking
showkey(1) and hitting that selfsame key.

                         -*-

Note: If you use tmux on top of the tty, you
might get this error with showkey:

    Couldn't get a file descriptor referring to the console

If so, do either

    $ sudo showkey                       # every time

or if that doesn't work/is inconvenient

    $ sudo chmod u+s /usr/bin/showkey    # once

If showkey is somewhere else than
/usr/bin/showkey, do

    $ type showkey

in bash (or zsh) to find out where it is.

                         -*-

Let's return to the line

    control keycode 11 = U+0110

This syntax reads: assign the shortcut C-0 so
that when pressed, instead of the normal
behavior it inserts the char which has Unicode
designation U+0110. That char turns out
a diamond in a tty, so it must be something
fancy that we'll never need for anything else.

The Unicode (the particular code, i.e. U+0110)
is arbitrary in the sense that it doesn't
matter what it is as long as the char isn't in
use already. Make it exotic! When you have
found one such exotic char, it is easy to find
several others just by adding one for each
shortcut you add. Just add one!
Classic comp-sci stuff. Yes, the notation
is hexadecimal.

                         -*-

Note: When I posted this tutorial on
      gmane.emacs.help, Yuri Kahn wrote that:

    > If you are going to recommend people to
    > hijack arbitrary Unicode characters for
    > extended keycodes, at least tell them to
    > pick codes from the "Private Use Area"
    > (U+E000 up to and including U+F8FF).
    > It is the Unicode equivalent of RFC 1918
    > IP addresses — guaranteed to never have
    > an official meaning.

                         -*-

Now save the remap.inc file and use this zsh
function (or a bash equivalent, or just type
the command) to bring up the modified keyboard
and see that it works:

    #! /bin/zsh
    lkeys () {
      loadkeys -q -c -s /etc/console-setup/remap.inc
    }

Again, do the '+s' thing if you don't want to
do sudo each time with loadkeys(1).

After invoking 'lkeys', hit C-0 in a tty. Now,
the diamond should appear!

                         -*-

Note: The options above to loadkeys are not
      relevant to this tutorial, but I use the
      function for other purposes as well, and
      it is bad luck to modify a function in
      a text document. Briefly, those options
      are:

    -c     --clearcompose
    -q     --quiet
    -s     --clearstrings

                         -*-

Next, in an Emacs init file - ~/.emacs, or if
you want to put such things somewhere else, and
then do `load-file' from the main init file -
anyway, in such a file, type:

    (define-key input-decode-map [?\u0110] [C-0])

The same Unicode position is used, only the
notation differs slightly. The "C-0" is an
arbitrary name, but it is a good name that is
descriptive and adheres to the Emacs notation
for keys.

Evaluate the `define-key' function.

Done! To try it, hit the key C-0, and it should
say:

    <C-0> (translated from diamond) is undefined

This means you can bind it to whatever, using
the ordinary Emacs syntax:

    (global-set-key  [C-0]  #'switch-to-buffer)

One last hint: Because you want to load the
modified keymap each time you start the system,
but without having to input the super user
password, one way to do that (at least on
Debian) is to put:

    loadkeys /etc/console-setup/remap.inc > /dev/null

in

    /etc/rc.local

On my Raspberry Pi Raspbian, another Debian
fork, I have it in ~/.zprofile instead.


Tutorial by: Emanuel Berg (moasenwood AT zoho DOT eu)
Last modified: July 21, 2015
               June 25, 2017