#!/usr/bin/perl

use strict;

my %old_hash = ( 'number' => '5',
                 'cat'    => '3',
                 'dog'    => '2'
               );

my %new_hash = reverse %old_hash;
my @sort_arrays = map { $old_hash{$_} }
                  sort { $old_hash{$a} <=> $old_hash{$b} }
                  (keys %old_hash);

print "$new_hash{$_} -> $_\n" for (@sort_arrays);