Watch-xi2 looks for X Window System events that occur when input device hierarchy changes in any way (e.g. when a keyboard or a mouse is connected or disconnected). It may take a single parameter: a shell command to run on the hierarchy change events.

watch-xi2.c

/* (c) Copyright 2010 Anton Kovalenko <anton@sw4me.com>.
   LICENSE:Do what you want with this software, but don't blame me.

   Compile it with gcc -lX11 -lXi.
*/
#define WATCH_XI2_TIMESTAMP "Time-stamp: <2010-08-14 19:39:55 anton>"
#include <X11/Xlib.h>
#include <X11/extensions/XInput2.h>
#include <X11/Xutil.h>
#include <stdio.h>
#include <stdlib.h>

#define EPIC_FAILF(format,...)  		\
  do {						\
    fprintf(stderr,format "\n",__VA_ARGS__);	\
    exit(1);					\
  } while (0)

#define EPIC_FAIL(string) EPIC_FAILF("%s",string)


void usage()
{
  EPIC_FAIL("\nwatch-xi2 [" WATCH_XI2_TIMESTAMP "]\n\n"
	    "Watch-xi2 looks for X Window System events that occur when \n"
	    "input device hierarchy changes in any way (e.g. when keyboard or\n"
	    "mouse is connected or disconnected).\n\n"
	    "It may take a single parameter: a shell command to run on the hierarchy\n"
	    "change events:\n\n"
	    "  watch-xi2 'xmodmap .my-xmodmap'\n\n"
	    "If no parameter is given, watch-xi2 just prints a line to stdout\n"
	    "instead of running anything.");
}


int main(int argc, char *argv[])
{
  Display *dpy;
  int major=2, minor=0, xi_opcode, event, error;
  XIEventMask interesting;
  Window root;

  if (argc != 1 && argc != 2 ||
      argc == 2 && argv[1][0]=='-')
    usage();
  
  dpy = XOpenDisplay(NULL);
  if (!dpy) 
    EPIC_FAIL("Can't open display");
  if (!XQueryExtension(dpy, "XInputExtension", &xi_opcode, &event, &error))
    EPIC_FAIL("X Input extension not available.");
  if (XIQueryVersion(dpy,&major,&minor)!=Success)
    EPIC_FAIL("XInput2 not supperted");
  root = DefaultRootWindow(dpy);
  interesting.deviceid = XIAllDevices;
  interesting.mask_len = XIMaskLen(XI_HierarchyChanged);
  interesting.mask = calloc(interesting.mask_len, sizeof(char));
  if (!interesting.mask)
    EPIC_FAIL("Out of memory");
  XISetMask(interesting.mask, XI_HierarchyChanged);
  XISelectEvents(dpy,root,&interesting,1);
  XSync(dpy,False);
  while (1) {
    XEvent xevent;
    XGenericEventCookie *cookie = (XGenericEventCookie*)&xevent.xcookie;

    XNextEvent(dpy,&xevent);
    if (XGetEventData(dpy,cookie) &&
	(cookie->type == GenericEvent) &&
	(cookie->extension == xi_opcode)) {
      if (argc<2) {
	puts("Something happened: please do something useful."); }
      else {
	printf("Running shell command %s...\n",argv[1]);
	system(argv[1]); }
      fflush(stdout);}}}

/* Local Variables: */
/* compile-command: "make LDFLAGS='-lX11 -lXi' CFLAGS='-O2' watch-xi2" */
/* End: */