check whether Nagle's algorithm is on or off

gistfile1.txt

#!/usr/bin/perl

# modified from the broken 'perldoc perlfunc' getsockopt example by adding one line (see comment below)

use strict;
use warnings;

use Socket qw(:all);

defined(my $tcp = getprotobyname("tcp"))
    or die "Could not determine the protocol number for tcp";
socket(my $socket, PF_INET, SOCK_STREAM, 0)
    or die "socket: $!"; # added this line
# my $tcp = IPPROTO_TCP; # Alternative
my $packed = getsockopt($socket, $tcp, TCP_NODELAY)
    or die "getsockopt TCP_NODELAY: $!";
my $nodelay = unpack("I", $packed);
print "Nagle's algorithm is turned ", $nodelay ? "off\n" : "on\n";