You most likely have tried to use a "telnet" connection in PuTTY, which results in some control characters being sent when the connection is established. You need a raw connection. Select "Raw" instead of "Telnet" when you create the connection, or try this from a command prompt (assuming putty.exe is in your path or in the current directory):

Then it works.

Secondly, have you considered using the OO interface to sockets in Perl? In can clean up your code significantly:

#!/usr/bin/perl

use strict;
use warnings;
use IO::Socket qw/:DEFAULT :crlf/;
use FileHandle;

use 5.014;

my $port = 6699;
my $server = IO::Socket::INET->new( Proto       => 'tcp',
                                    LocalHost   => 'localhost',
                                    LocalPort   => $port,
                                    Listen      => 1,
                                    Reuse       => 1);
die "Server setup failed: $!" unless $server;

say "starting on port: $port...";

while (my $client = $server->accept()) {
    print $client "ready$CRLF";
    local $/ = LF;  # Be robust about accepting LF or CRLF endings on 
+input
    CLIENT: while (<$client>) {
        s/$CR?$LF//;    # chomp CRLF or LF
        say "Client request: `$_'";
        for ($_) {
            print $client "help!$CRLF" when /^help/;
            last CLIENT                when 'quit';
        }
    }
    say "Disconnected";
}
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