How to map Caps Lock as the compose key using Xmodmap portably and idempotently

xmodmap

I can't seem to find a way to use Caps Lock as the compose key properly. Some methods are not portable since they require that you detect the key number using something like xev on every host. Other methods result in a ~/.Xmodmap which cannot be passed to xmodmap more than once without bad keysym and similar errors. This makes it difficult to test changes to the file. Is there some way to do this in ~/.Xmodmap?

Best Answer

You are having problems with idempotency because you are using keysym instead of keycode. Think of keycode as being an assignment of a key to a function, while keysym is just a link from a function name to an actual function.

When you use keysym as follows:

keysym Caps_Lock = Multi_key

you essentially delete the name Caps_Lock. Therefore, the next time you run xmodmap and you reference Caps_Lock in this same line, it gets confused.

The correct way to do it is to reassign the keycode directly as follows:

keycode 66 = Multi_key

You can get the keycode from the xev command for example.

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keyboard x11 xmodmap xkb – Assign Another Modifier to Alt Key for X11

(This answer is about xmodmap only. I'm sure it's possible to do this with XKB, I just don't know how.)

Modifiers and keysyms are assigned independently. But you get strange effects if you don't set them consistently. I think all you're missing is the add command to assign a modifier to Meta_L, though you may also need to clear and reassign the modifier keys. You may replace Mod1 and Mod2 by Mod3, Mod4 and Mod5: they are interchangeable, just make sure you don't use one for two different purposes.

clear Mod1
clear Mod2
remove Lock = Caps_Lock
keysym Caps_Lock = Alt_L
keysym Alt_L = Meta_L
add Mod1 = Alt_L Alt_R
add Mod2 = Meta_L Meta_R

Remapping Caps Lock with Xmodmap Doesn’t Work – Fix

The xmodmap(1) man page has an example for exactly this

   !
   ! Swap Caps_Lock and Control_L
   !
   remove Lock = Caps_Lock
   remove Control = Control_L
   keysym Control_L = Caps_Lock
   keysym Caps_Lock = Control_L
   add Lock = Caps_Lock
   add Control = Control_L

but if you want to finish doing it the way you started, I think you need to add at least the remove and add lines

   remove Lock = Caps_Lock
   remove Control = Control_L
   keycode 37 = Caps_Lock
   keycode 66 = Control_L
   add Lock = Caps_Lock
   add Control = Control_L

I'm guessing that's the case based on this paragraph

   add MODIFIERNAME = KEYSYMNAME ...
           This adds all keys containing the given keysyms  to  the  indi‐
           cated  modifier  map.  The keysym names are evaluated after all
           input expressions are read to make it easy to write expressions
           to swap keys (see the EXAMPLES section).

which makes it sound like modifier changes (shift, control, etc.) don't get applied until you run that too.

(And logically the same with remove)

The keycode version has the advantage of being idempotent, meaning that the effect won't change if xmodmap is run multiple times.

Best Answer

Related Solutions

keyboard x11 xmodmap xkb – Assign Another Modifier to Alt Key for X11

Remapping Caps Lock with Xmodmap Doesn’t Work – Fix

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