close_wait.pl

use v5.14;                                                                                                                                                                   [6/1836]
use warnings;

use IO::Socket;
use POSIX qw(:sys_wait_h);

my($ip, $host) = @ARGV;

my $sock = IO::Socket::INET->new(
    PeerAddr => "$ip:80",
    Proto    => "tcp",
) or die($!);

say "Parent: connected";

my $netstat = "netstat -n | grep $ip || echo nothing";

if(my $pid = fork()) {
    my $terminated = 0;

    $SIG{CHLD} = sub {
        my $pid2 = waitpid(-1, WNOHANG);
        if($pid == $pid2) {
            $terminated = 1;
        }
    };

    $sock->send(join(
        "\r\n",
        "GET / HTTP/1.1",
        "Host: $host",
        "Connection: close",
        "\r\n"
    ));
    $sock->recv(my $buf, 42);
    say "Parent: received ${\length $buf} bytes";
    $sock->close;
    say "Parent: close()";

    1 while not $terminated;
}
else {
    sleep(3);
    say "Child: before close()";
    system($netstat);

    say "\n<Enter> to close() in the child";
    <>;
    $sock->close;

    say "Child: after close()";
    system($netstat);
}