# example input string
$in = '1089,3,4,5,6,7,99,832,1087,831,1088';

@i = split(/,/,$in);

# resort the array numerically
@read = sort by_number @i;

$list = '';

foreach $i (0..$#read) {
	if(($read[$i]+1) == $read[$i+1]) {
		$list .= $read[$i].'-'.$read[$i+1].',';
	} else {
		$list .= $read[$i].',';
	}
}

$list =~ s/(\d+)\,\1\-/\1\,/g;

# output the finished product
print $list;

# again, credit to ncw for the sort method
sub by_number
{
    my @a = split /(\d+)/, $a;
    my @b = split /(\d+)/, $b;
    while (@a && @b)
    {
        my ($aa, $bb) = (shift(@a), shift(@b));
        my $res = ($aa =~ /^\d/ && $bb =~ /^\d/) ?
            $aa <=> $bb :
            $aa cmp $bb ;
        return $res if $res;
    }
    return @a <=> @b;
}