#!/usr/bin/perl -w
use strict;

use Inline(C  => Config =>
    INC => '-I/usr/local/include',
    AUTO_INCLUDE => '#include <X11/Xlib.h>',
    LIBS         => '-L/usr/X11R6/lib -lX11',
    CCFLAGS      => '-O2'
);

use Inline C => <<'END_OF_C_CODE';
 
int isXRunning()
{
 Display* display;
 char* displayName;
 int retval = 0;

 displayName = getenv("DISPLAY");
 if (!displayName)
 {
  displayName = "localhost:0";
 }

 display = XOpenDisplay(displayName);
 if (display)
 {
  XCloseDisplay(display);
  retval = 1;
 }
 return retval;
}

END_OF_C_CODE

print isXRunning() ? "X is running\n" : "What X?\n";