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

sub get_data {
  # here we simulate the expensive operation 
  # of loading data into the hash
  my $idx = shift;
  print "retrieving data for $idx...\n";
  return "value for $idx";
}
my $result;
my %cache;
foreach (1,2,4,16,32,2,64,1,2) {
  # here we are asking for values from the cache
  # (hash), and if they aren't there, we get them
  # from the file.
  $result = $cache{$_} ||= get_data($_);
  print "$result\n";
}

##</code><code>##

retrieving data for 1...
value for 1
retrieving data for 2...
value for 2
retrieving data for 4...
value for 4
retrieving data for 16...
value for 16
retrieving data for 32...
value for 32
value for 2
retrieving data for 64...
value for 64
value for 1
value for 2