d20 dice roller

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

sub roll { return int(1+rand($_[0])); }

# Interprets expressions like "6x3of4d6+2"
sub dice {
    my $spec = shift;
    die "bad dice expression" if
	$spec !~ 
	m/(?:(\d+)x)?        # repeat N times
	  (?:(\d+)of)?       # select top N dice
	  (?:(\d+))?         # count of dice to roll
	  d(\d+)             # die type, only field required
	  (?:([\-+]\d+))?/x; # add/subtract offset

    my ($repeat, $select, $count, $type, $off) = ($1, $2, $3, $4, $5);
    if(!defined $repeat or $repeat eq "") { $repeat = 1; }
    if(!defined $count or $count eq "") { $count = 1; }
    if(!defined $select or $select eq "") { $select = $count; }
    if(!defined $off or $off eq "") { $off = 0; }

    my @raw_rolls = ();
    my @results = ();
    for(my $rep=0; $rep<$repeat; $rep++) {
	my @rolls = ();
	for(my $roll=0; $roll<$count; $roll++) {
	    my $val = roll($type);
	    push @raw_rolls, $val;
	    push @rolls, $val;
	}
	@rolls = sort {$a<=>$b} @rolls;
	for(my $i=$select; $i<$count; $i++) { pop @rolls; }
	my $total = $off;
	foreach my $r (@rolls) { $total += $r; }
	push @results, $total;
    }
    print "Results:";
    foreach my $r (@results) { print " $r"; }
    print " (raw rolls:";
    foreach my $r (@raw_rolls) { print " $r"; }
    print ")\n";
}

foreach my $s (@ARGV) { dice($s); }