#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

sub sort_hash (&\%) {
    my ($sub, $hash) = @_;
    sort {
        local($a, $b) = @$hash{$a, $b};
        $sub->()
    } keys %$hash
}

my %hash = ( second => 2, fourth => 4, third => 3, first => 1 );
say for sort_hash { $a <=> $b } %hash;