Here's another anti-social snippet for you to look at. :-)

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

my $main = MainWindow->new(-title => "Resize Test");
$main->geometry("600x400+100+100");

$main->Button(
   -text => "Exit Program",
   -command => sub { exit }
  )->pack();

my $button = $main->Button(
         -text => "Go To Fullscreen",
         -command => \&resizer,
  )->pack();

MainLoop; 

sub resizer{ 

  if ( $button->cget(-text) =~ /Fullscreen/ ){
  
     $main->geometry($main->screenwidth . 'x' .
             $main->screenheight . '+0+0');
     $button->configure(-text=>"Go to Window");
    }else{
      $main->geometry("600x400+100+100");  
      $button->configure(-text=>"Go To Fullscreen");

    }

}
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