use strict;
use warnings;
use Tk;

my $main = Tk::MainWindow->new (-title => 'Resize demo');

$main->Button (
    -text => 'Change size',
    -command => sub {ChangeSize ($main, @_)},
)->pack ();

MainLoop ();

sub ChangeSize {
    my ($wind) = @_;
    my $newSize = int (100 + rand (100)) . 'x100+100+100';
    
    $wind->geometry ($newSize);
}