while ($line = <IN>)
{$nextline=<IN>;

##</code><code>##

my $previous = '';
while ($line = <IN>) {
     if ($line =~ /mamma/ && $line =~ /mia/) {
          print OUT $previous;
          print OUT $line;
     } else {
          print ".";
     }
} continue {
    $previous = $line;
}