$mw = $f1->Entry(
             -textvariable => '',
            -width => 40);
$mw->pack(-side => "left");

##</code><code>##

my $f1_value;
$mw = $f1->Entry(
             -textvariable => \$f1_value,
            -width => 40);
$mw->pack(-side => "left");