#!/usr/bin/perl

use strict;
use warnings;

my %hash = (
    '[foo]' => [3],
    '[bar]' => [2],
    '[buz]' => [1],
    '[qiz]' => [undef],
);

print 'K: '. $_ .' V: '. $hash{$_}->[0] . "\n" for 
    sort { $hash{$a}->[0] <=> $hash{$b}->[0] } 
    grep { defined $hash{$_}->[0] } 
    keys %hash;