file 1
------
a 0
c 1
d 1
e 3
f 0

file 2
------
a 0
b 0
c 0
d 0
e 0
f 0

##</code><code>##

file3
-----
a 0
b 0
c 1
d 1
e 3
f 0

##</code><code>##

   open FIRST,"file1" or die "Can't open file1: $!\n";
   open LAST,"file2" or die "Can't open file2: $!\n";
   open NEW,">file3" or die "Can't open file3: $!\n";
   chomp (my @last=<LAST>);
   
   my %names;
   @names {<FIRST>} = ();

   foreach my $name (@last) {
      next if exists $names { $name }or
      print NEW "$name\n";
   }

   close FIRST;
   close LAST;
   close NEW;