foreach my $file(@files){
  open(TMP, '>/tmp/temp.html') || die "tmp file open failed:$!\n";
  open(FILE, "$file") || die "source file open failed: $!\n";
  while(<FILE>){
    s/<title>(.+)<\/title>/<title>$new_title<\/title>/i;
    print TMP $_;
  }
  close(TMP);
  close(FILE);

  unlink($file);
  rename('/tmp/temp.html', $file);
}