How can I write a "idempotent" .Xmodmap

Question

Currently I have an .Xmodmap file that changes my Command to Ctrl, then changes my Ctrl to Super (I'm running Linux on a Mac).

It works quite well, when only run once but on successive runs (for example when I restart my desktop environment (Cinnamon) it reloads the .Xmodmap file) it basically resets the settings by reverting the changes. Effectively toggling between my desired setup and the original setup.

How can I write an .Xmodmap file that only sets the settings one time, but doesn't change them back on successive runs? Here is my existing .Xmodmap file:

clear control
clear mod4

keycode 105 =
keycode 206 =

keycode 133 = Control_L NoSymbol Control_L
keycode 134 = Control_R NoSymbol Control_R
keycode 37 = Super_L NoSymbol Super_L

add control = Control_L
add control = Control_R

Answer 1

Reset the map to its original state before applying your mods. A full reset takes forever, so best I can come up with is diffing.

This code uses .Xmodmap{.orig,.reset,.mods} where if .orig doesn't exist it's set to the current state, and calculates .reset to restore that state from wherever it's got to. before applying .mods.

#!/bin/sh
# file xmodmap-reset

#     rm ~/.Xmodmap.orig
# beforehand to take current setup as baseline for Xmodmap.mods changes

stem=~/.Xmodmap
orig=${stem}.orig
reset=${stem}.reset
mods=${stem}.mods

# implement -pme like -pke
#
xmodmap-pme () {
  xmodmap -pm \
  | sed '
        1d
        / [^ ]/!d
        s/^[^ ][^ ]*/clear &\nadd & =/
        s/([^ ]*//g
    '
}

# save baseline if none atm
test -a $orig || {
    xmodmap  -pke
    xmodmap-pme
} > $orig

# payload, diff for commands to reset to baseline from current
{
    xmodmap  -pke
    xmodmap-pme
} \
| {
    diff -u0 $orig - \
    | sed -n '
        1,/^@@/d
        s/^[^+]clear/clear/p
        s/^-//p
      '
} > $reset
xmodmap $reset

# finally ready to apply the mods
test -a $mods && xmodmap $mods

(edit: cleanup)

Answer 2

Go to system > Preferences > Startup Applications and add xmodmap ~/.Xmodmap.

Answer 3

I'm still confused a little bit as to what you want, but I think this it:

If you put this in your ~/.Xmodmap,

clear control
clear mod4

keysym Super_L = Control_L
keysym Control_L = Super_L

add control = Control_L
add control = Control_R
add mod4 = Super_L
add mod4 = Super_R

then every time xmodmap ~/.Xmodmap is executed, then the left Ctrl and left ⌘ key swap. So, on the first invocation, the Ctrl key acts as though you pressed ⌘, but on the second invocation, it resumes acting as a Ctrl key again.