use Tk;
use Tk::Dialog;
use strict;
use warnings;

my $top = new MainWindow(-title => "demo");	
my $save = $top->Button(-text => "Close", command => \&process_save)->pack();
MainLoop;

sub process_save {
	my $dialog = $top->Dialog(-title => "Save?", -text =>  "Content changed, save the changes?", -buttons => ["OK", "Cancel"]);#in real world, you only display this, if the content changed
	my $response = $dialog->Show();
	print $response, "\n" #in real code, handle the response...
}