#!/usr/bin/perl -w
use strict;

my @special_order = ("x", "b", "a", "y");
my $i =0;
my %sort_order = map{$_ => $i++}@special_order;

my @array = ("a", "x", "y", "b");
@array = sort @array;
print "Regular Sort: @array\n";

@array = ("a", "x", "y", "b");
@array = sort by_order @array;
print "Special Sort: @array\n";

sub by_order
{
   my $a_order = $sort_order{$a};
   my $b_order = $sort_order{$b};
        $a_order <=> $b_order
}

__END__
prints:
Regular Sort: a b x y
Special Sort: x b a y