my %ports = (
  3010 => 3100,
  3020 => 3200,
  3030 => 3300,
  3040 => 3400,
  3050 => 3500,
);

my $port = "3030";
unless (exists $ports{$port}) {
    print "no port\n";
}
else {
  my $port2 = $ports{$port};
  print $port2;
}