# $n contains field to sort on
# records to sort are in @ARGV
my @records;
while (<>) {
  # chomp deleted so we don't have to add \n later
  push @records, [ split ',' ];
}
# now sort them;
@records = sort { $$a[$n] cmp $$b[$n] } @records;
# now print them
foreach $record (@records) {
  print join (',',@$record);
}