# initialize an Expect object:
my $conn = Expect->new;
$conn->raw_pty(1);

# spawn a new SSH process:
$conn->spawn('/usr/bin/ssh', -l => $user, $host, -s => 'sftp')
    or die $errstr;

# wait for the password prompt:
$conn->expect($timeout, "Password:")
    or die "Password not requested as expected";

$conn->send("$passwd\n");

# SSH echoes the "\n" after the password, remove it from the stream:
$conn->expect($timeout, "\n");