for (0..$#line2) {
   my $i = $line2[$_];
   for (0..$#line1) {
      my $j = $line1[$_];
      print $i if if $i eq $j;
   }
}

##</code><code>##

my %lookup;
++$lookup{$_} for @line2;

for (@line1) {
   print if $lookup{$_};
}

##</code><code>##

my %lookup;
$lookup{$_} = -1 for @line2;

for (@line1) {
   print if !++$lookup{$_};
}