use Symbol qw(gensym);
use Device::SerialPort;
(etc.)
my $port, $handle;
$handle = gensym();
$port = tie(*$handle, "Device::SerialPort", "/dev/ttyUSB0");
$port->baudrate(57600);
(etc.)

##</code><code>##

$port->close;
undef $port;
untie *$handle;

##</code><code>##

<fh> select error: Bad file descriptor (hits=-1)