For example :
$keys{a} = 2;
$keys{b} = 1;
$keys{c} = 12;
$keys{d} = 'a12';
$keys{d} = 'a9';

# 3 = sort by value - numeric ascending- will not work if contain characters

  foreach my $key (sort {$keys{$a} <eq> $keys{$b} || length($a) <=> length($b) || $a cmp $b} (keys %keys)) 
  {
    print "Key = $key, Value = $keys{$key}\n";
  }