#!/usr/bin/perl

use strict;
use Tk;

my $mw = MainWindow->new();

my $txtvar;  # have a separate scalar for each Entry widget

$mw->Entry(-textvariable=>\$txtvar # this is the trick
           )->pack();

$mw->Button(-text=>"Print & Clear",
            -command=>sub{print $txtvar,$/; $txtvar=""}
            )->pack();

MainLoop;