Woxidu

Recently I needed to write a script that changed its behavior when the shift-key was held down. After some research to find a pre-made (and command-line-friendly) solution, I gave up and decided to rip open xkbwatch and see how it does it. It turned out not to be so scary and so I extracted the meaningful bits of code from it and condensed it into a more general-purpose tool. Let me know if I overlooked a really easy or simple way of doing this.

/*
** xkbdump.c
** Dumps the modifier keys onto the command line in a space-separated list.
*/
#include <stdio.h>
#include <X11/Xlib.h>
#include <X11/XKBlib.h>

int main()
{
    Display *dpy = XOpenDisplay(0);
    XkbStateRec state; // I don't fully understand this structure. 
                       // I only know that it reports my modifier keys.
    XkbGetState(dpy, XkbUseCoreKbd, &state);

    int i;
    for (i = 0; i < (sizeof(state.mods) * 8); ++i)
        if ((1 << i) & state.mods)
            printf("%d ", (1 << i) & state.mods);
    printf("\n");
    return 0;
}

The use-case I had imagined was something like this.

#!/usr/bin/env bash

SHIFT_KEYCODE=1
CTRL_KEYCODE=4
# ^ Inferred above just by running xkbdump with ctrl/shift held down

both_held=$(xkbdump | grep "\<$SHIFT_KEYCODE\>" | grep "\<$CTRL_KEYCODE\>");
shift_held=$(xkbdump | grep "\<$SHIFT_KEYCODE\>");
ctrl_held=$(xkbdump | grep "\<$CTRL_KEYCODE\>");

if [ "$both_held" ]; then echo "Both shift and control were held down";
elif [ "$shift_held" ]; then echo "Only shift was held down";
elif [ "$ctrl_held" ]; then echo "Only control was held down";
else echo "Neither shift nor control were held down";
fi

One last note. In order to build this, you need to tell gcc where to link against X11. Build with a gcc command like this.

gcc xkbdump.c -o xkbdump -lX11