You could work with -textvariable (instead of -text) which binds a reference to a variable to the content of the entry, e.g

use vars qw($InputText);
$InputText = "";
...
my $input = $mw->Entry (-textvariable => \$InputText)->form;
...
# my $guess = int ($input->get);
my $guess = int( $InputText );
$InputText = ""; # empty it
[download]

Another Idea: If you just want to allow integer values to be entered, it often is a good way not to allow other input than numbers which makes errorchecking easier. Maybe Tk::NumEntry could be interesting for you, or my Tk::EntryCheck, e.g.

my $input = $mw->EntryCheck(
  -textvariable => \$InputText,
  -pattern      => qr~\d~,
)->form;
[download]