johngg@shiraz:~ > perl -Mstrict -Mwarnings -MData::Dumper -E '
my $idStr = q{381980767204};
my %idLookup =
   map { $_ => 1 }
   unpack q{(a4)*}, $idStr;
print Data::Dumper->Dumpxs( [ \ %idLookup ], [ qw{ *idLookup } ] );
say qq{ID $_ }, exists $idLookup{ $_ } ? q{found} : q{not found}
   for qw{ 7204 6720 };'
%idLookup = (
              '8076' => 1,
              '7204' => 1,
              '3819' => 1
            );
ID 7204 found
ID 6720 not found