...
# Create controls

$event_field->Append("Initializing modem... ");

init_modem();

$event_field->Append("initialized\n");

$card_input->SetFocus();

$event_field->Append("Please swipe card... ");

$window->Show();

Win32::GUI::Dialog();

sub card_input_Change {
    my $input1 = $card_input->GetLine(0);
    my $input2 = $card_input->GetLine(1);

    $event_field->Append("swiped\n");

    print "\$input1: $input1\n";
    print "\$input2: $input2\n";

    my $cc_number;
    if ($input1 =~ /^\%B(\d{16})/i) {
        $cc_number = $1;
    }

    my $exp_dt;
    if ($input2 =~ /\=(\d{2})(\d{2})(.*)/) {
        $exp_dt = $2 . $1;
    }

    sleep 1;

    $event_field->Append("Connecting... ");

    ...
}