#!/usr/bin/perl -wT
use strict;
use DB_File;

my $dbmfile = '/tmp/lookuptable';

tie my %lookuptable, "DB_File", $dbmfile, O_RDWR|O_CREAT, 0640, $DB_HASH
      or die "Cannot open file '$dbmfile': $!\n";

# do whatever it is to get the ids...
my $id = '123456789';

# check lookup cache:
my $cachevalue = $lookuptable{$id};

if ($cachevalue eq 'Y') {
   # link is ok
} elsif ($cachevalue eq 'N') {
   # link is bad
} else {
   # determine if it is good or bad.
   my $isok = 'Y';

   # add the calculated value to the cache
   $lookuptable{$id} = $isok
}