#/usr/bin/perl
use warnings;
use strict;

my %hash = (a => 4,
            b => 6,
            c => 2);
            
my @sorted_keys = sort keys %hash;
print "@sorted_keys\n";

my @sort_by_value = sort{my $A = $hash{$a};
                         my $B = $hash{$b};
                            $A <=> $B  ## or cmp for strings
                        }keys %hash;
                        
print "@sort_by_value\n";

__END__
Prints:
a b c  # simple key sort
c a b  # keys sorted by value of keys