#!/usr/bin/perl --
use strict;
use warnings;
use Data::Dump qw/ dd pp /;

open my($fh),'<', \<<'__FUDGE__' or die;
STORE     PRODUCT_ID
====================
Sydney    12
Sydney    14
Canberra  12
Canberra  18
__FUDGE__

my %hash;
$hash{(split)[0]}{(split)[1]} = 1 while <$fh>;
seek $fh, 0, 0;

dd\%hash;
undef %hash;

map {
    my @explicit  = split ' ', $_;
    2 == @explicit ## ====
        and $hash{ $explicit[0] }{ $explicit[1] }++;
    ();
} <$fh>;

dd\%hash;
__END__
$ perl fudge
Use of uninitialized value in hash element at fudge line 16, <$fh> line 6.
{
  "====================" => { "" => 1 },
  "Canberra" => { 12 => 1, 18 => 1 },
  "STORE" => { PRODUCT_ID => 1 },
  "Sydney" => { 12 => 1, 14 => 1 },
}
{
  Canberra => { 12 => 1, 18 => 1 },
  STORE    => { PRODUCT_ID => 1 },
  Sydney   => { 12 => 1, 14 => 1 },
}