while (<>) {
   my ($node) = split /,/;
   open $node, ">>$node" or die "a horrible death!";
   print $node $_;
   close $node;
}

##</code><code>##

my %cache;
while (<>) {
   my ($node) = split /,/;
   unless ($cache{$node}) {
      open $node,">>$node" or die "a horrible death";
      $cache{$node}++;
   }
   print $node $_;
}
for my $n (keys %cache) { close $n; }