# untested

while (<$first_fh>){
      chomp;
      my %infirst;
      # every word become a key of temporary hash
      map{$infirst{$_}++} split ' ',$_;

      my $ref_line = <$second_fh>;
      chomp $ref_line;
      print grep {exists $infirst{$_}} split ' ',$ref_line;

      die "$file_one exhausted!" if eof($first_fh);
      die "$file_two exhausted!" if eof($second_fh);
}