Ah. I gathered from your original post (assuming you are jtx) that it was always client, server in strict alternation. If that's not the case, you might be able to use select to determine whether there is data waiting to be read. I believe POE can do this sort of stuff relatively easily, though it may well be overkill.

What I have been able to do, though it is a cheap hack and will probably have to be re-written if I want this to be a serious program, is taken your idea of using a while loop and somewhat modifying the server/client. This is the modified client, and it works, though like I said, I think it's pretty cheesy:

#!/usr/bin/perl

use IO::Socket;

# Make our connections
my $ns1 = new IO::Socket::INET (PeerAddr  => 'ns1',
                                PeerPort  => 1200,
                                Proto     => 'tcp'
                               ) or die "Couldn't create socket: $!\n"
+;

my $line;
my $count = 0;

my $domain = 'hello.com';
my $ipaddress = '192.168.0.1';

while ($line ne 'CAIO') {

   if ($count == 0) {
      print $ns1 "HELO\n";
      $count++;
   } elsif ($count == 1) {
      print $ns1 "dom:$domain\n";
      $count++;
   } elsif ($count == 2) {
      print $ns1 "ipaddr:$ipaddress\n";
      $count++;
   } elsif ($count == 3) {
      print $ns1 "addzone\n";
      $count++;
   }

   sleep(1);
   chomp($line = <$ns1>);
   print "$line\n";
}

close($ns1);
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As you might have gathered, the server is a name server, and this program was created to add zones via sockets. It's irrelevant to me at this point whether or not BIND supports this natively - This is just a good way for me to practice using Sockets and TK, and make my boss happy while I write programs that will eventually end up being my replacement :)

Or:

my (@cmds) = ("HELO", "dom:$domain", "ipaddr:$ipaddress", "addzone");

while (@cmds)
{
    print $ns1 shift(@cmds), "\n";
    $line = <$ns1>;          # don't need the sleep;
                             # the read should block until
                             # a line is available.

    defined($line) or last;  # quit if connection closed
                             # (could die instead)

    print $line;             # don't need \n now, $line
                             # not chomped

    ($line =~ /^CAIO$/) and last;
                             # $ can handle trailing
                             # newline, with no
                             # significant speed penalty
                             # (should be optimized by
                             #  regex engine)
}
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