use strict;
use warnings;

use IO::Socket::INET;
use IO::Select;

my $Port = 2005;

my $server = IO::Socket::INET->new(
  LocalPort => $Port,
  type => SOCK_STREAM,
  Reuse => 1,
  Listen => 10
) or die "Server läuft nicht: $@\n";

my $select = IO::Select->new($server);

while (my @readable = $select->can_read) {
  for my $socket (@readable) {
    if ($socket == $server) {
      print "New client connects\n";
      my $client = $socket->accept;
      $select->add($client);
    }
    else {
      my $byte = $socket->getc;
      if (defined $byte) {

        print "$byte\n";

        if ($byte eq "!") { $socket->print("\$OK!"); }
      }
      else {
        print "Connection closed by client\n";
        delete_socket($select, $socket);
      }
    }
  }
}

sub delete_socket {...}