# untested code
use Socket qw(IPPROTO_TCP)
my $has_nagle = eval "Socket::TCP_NODELAY(); 1";
...
if ($has_nagle) {
    setsockopt($fh, IPPROTO_TCP, 
               Socket::TCP_NODELAY(), 1) ||
            croak "Couldn't disable Nagle's algorithm: $!";
} else {
    warn("Your system doesn't seem to support turning of Nagle's algorithm\n");
}