GUI Perl

#!/usr/bin/perl -w
use Tk;
$both_sides = "single";
$single_sides = "double";
$main = MainWindow->new();
$label = $main->Label(-text => "Print Options");
$label->pack();
$frame = $main->Frame(-relief=>"groove",
                      -borderwidth=>2);
$check1 = $frame->Checkbutton(-text=>"Both Sides",
                              -variable=>\$both_sides,
                              -onvalue=>"both",
                              -offvalue=>"single");
$check1->pack(-side=>"top");
$check2 = $frame->Checkbutton(-text=>"Single Sides",
                              -variable=>\$single_sides,
                              -onvalue=>"both",
                              -offvalue=>"single");
$check2->pack(-side=>"top");
$frame->pack();
$button = $main->Button(-text => "Exit",
                        -command => \&exit_button);
$button->pack();
MainLoop();
sub exit_button {
    if ( $both_sides eq "both") {
        print "Print both sides.\n";
    } else {
        print "Print single-sided.\n";
    }
    if ( $single_sides eq "both") {
        print "Print both sides.\n";
    } else {
        print "Print single-sided.\n";
    }    
    exit;
}