sub num_or_str {
    no warnings 'numeric'; 
    $_[0] <=> $_[1] || $_[0] cmp $_[1]
}

my @sorted 
  = sort num_or_str( 
            $people{$a}->{age}, 
            $people{$b}->{age} 
         ), keys %people;

##</code><code>##

my @stuff = qw/ 9 -1 -3 hi 0 bye 5 10 /;

my $descending = 1;
my @ar;

if ( $descending ) {
       @ar = sort { num_or_str($b, $a) } @stuff;
}
else {
       @ar = sort { num_or_str($a, $b) } @stuff;
}

##</code><code>##

my $sort_by = 'age';
my $descending = 1;
my $database = \%people;

# return an ordered list of copies of keys of a 
# hash structured as described somewhere
# usage: sort_people( \%sort_me, $by_me, $descending )
# Ascending sort is the default.
# If $by_me is not a key that exists then ...
# Maybe an arref should be returned.
sub sort_people {
    my ( $people, $by, $desc) = @_;
    no warnings qw/ numeric uninitialized/;
    if ( $desc) {
        return sort { your_conditions( $b, $a)} keys %$people;
    } else {
        return sort { your_conditions( $a, $b)} keys %$people;
    }
} 

##</code><code>##

my @sorted_keys = sort_people( \%people, $sort_on, $descending);