#!/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";
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No, you can have $DISPLAY set and not have X running. I've seen $DISPLAY set by login scripts before (not uncommon when the display is on a remote machine). Try this from a text console without X running:


bash$ export DISPLAY=localhost:0
bash$ echo $DISPLAY
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Remember, your X server may not be on the local machine. I keep my $DISPLAY variable set on my embedded machines so I can run X programs on them at will, but don't actually start window managers for them, so most of the time $DISPLAY is set but the server might or might not be available.

Also, you can have X running but not have a $DISPLAY environment variable set (like if you go to a text console on the same machine).

This brings up the question of "what do you mean 'X running'?". Do you mean: is there one or more X servers going on this or some other machine, or is this program being run from within an X session? These are both tricky. My program just looks for a running X server at either $DISPLAY or localhost:0; if a server is not available, it returns 0.

Oh yeah...

I guess i need to read up on how X works! Thanks for the tips, monks!