my @range = (50000 .. 65535);
my @ports = (50000..51545,51549,51555..51999,@more);

##</code><code>##

my @hash{@ports} = (1) x @ports; #set indices to true for ports in use
my $open_port;
foreach my $port (@range){
   $open_port = $port and last unless $hash{$port};
}