use strict;
use warnings;

my %hash = ( 
    one   => 1, 
    two   => 2, 
    three => 3, 
    four  => 4, 
    five  => 5 
);

my $priority_key = 'three';

sub prioritize {
    my( $href, $find ) = @_;
    my @prioritized_keys;
    while( my( $key, $value ) = each %{$href} ) {
        if( $key ne $find ) {
            push @prioritized_keys, $key;
        } else {
            unshift @prioritized_keys, $key;
        }
    }
    return \@prioritized_keys;
}

my @keyset = @{ prioritize( \%hash, $priority_key ) };

print "@keyset\n";