X11/xorg map ctrl j (or ctrl m) to return; OR control codes in GUI / X11

Question

Terminal application and editors like vim (and emacs I think) make good use of control codes. I.e. Ctrl + M is carriage return and Ctrl + J is line feed. Both of these can be used to insert new lines in vim, or execute commands in shell. They are considerably more comfortable to press than return on basically all keyboards (when Ctrl is remapped to Caps lock at least).

On GUI applications that does not work, and it is annoying as hell. I use Opera as my browser and I tried configuring some support for that, but it only works in some elements. Of course it does not work in other applications.

Does anyone know how to make 'control code' bindings in X to make them act as special characters?
(Ctrl + H for backspace is also very very cool)

Answer 1

It's possible using xkb. You will have to create a custom keyboard layout and assign Ctrl (Caps Lock) to be your Level 3 shift key (sometimes called AltGr after its default location). Then set the 3rd level for M to the keysym for CR, J to LF, etc.. It's probably also possible to set up Backspace (using the function keysym, not the Unicode code point).

If you use AltGr (right Alt) in your preferred keyboard layout (e.g. for international characters), this will interfere. There reportedly also exists a Level 5 shift independent of AltGr, so set Ctrl/CapsLk as your level 5 shift instead (disclaimer: I haven't tried this).

There are several tutorials for doing this; here's one.

But if you're making your own layout, also consider just remapping keys you find difficult (e.g. if you never use Right Win, remap Enter onto it where your thumb/pinkie can easily access it).

_{Incidentally, how can CapsLk+key possibly be easier to press than Enter? It's perfectly symmetric between the hands, except you have to simultaneously press another key.}