#!/usr/bin/perl
use strict;
use warnings;

my (%ilb, %abs);
for my $key (qw/foo bar baz/) {
    $abs{$key} = {};
}
for my $key (qw/blah baz asdf/) {
    $ilb{$key} = {pos => $key, abs => (defined $abs{$key} ? 1 : 0)};
}