Here is a little script using Tk's eventloop to watch a file. You could modify it to watch your directory, or whatever files you want.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

#read  (perldoc -f stat). 

my $file = shift or die "No file given $!\n";
my $timer;
my $lastmtime = (stat $file)[9];

my $mw= tkinit;
$mw->withdraw;   #make it in background 
$mw->geometry('+20+20'); #set in upper left corner 

my $label = $mw->Label(
       -text => "$file modified at $lastmtime ")->pack(-expand =>1);

&startwatchdog($lastmtime);

$mw->Button(-text => 'Ok',
            -command => sub{
                    $mw->withdraw;
                    $timer->cancel;
                    &startwatchdog( $lastmtime );
                })->pack();
MainLoop;

sub startwatchdog{
my $mtime = shift;

$timer = $mw->repeat(5000, sub { # check every 5 seconds. 
             if ((stat $file)[9] > $lastmtime) {
                # file was modified. 
                # create your dialog box. 
                $lastmtime = (stat $file)[9];
                print "file modified at $lastmtime \n", chr(07);
                $label->configure(-text =>"$file modified at $lastmtim
+e");
                $mw->deiconify;
                $mw->raise;
         }
  });


}
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