#!/usr/bin/perl -w
use strict;
use Tk;

my $scale_var = 0;
my $entry_var;
my $main = MainWindow->new();
my $entry = $main->Entry(-textvariable => \$entry_var,
                         )->pack();
my $scale = $main->Scale(-variable => \$scale_var,
                         -length => '100p',
                         -from => 0,
                         -to => 100,
                         -command => sub { $entry_var = $scale_var },
                         )->pack();
$entry->bind( '<Return>', sub {
    if ( $entry_var =~ /^\d+$/ && $entry_var <= 100 ) {
        $scale_var = $entry_var;
    } else {
        print STDOUT "\a\a";
        $entry->delete( 0, 'end' );
    }
} );

MainLoop;