if <TITLE> and </TITLE> are on the same line always this would work

if(/<title>(.+)<\/title>/i){
  print $1;
  $notitle = 0;
  last;
}
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As for opening the file for appending, that probably isn't what you want to do. Open the source file and a temp file. Read from the source file, then write out each line(modified/unmodified) to the temp file. unlink() the source file, and rename the temp file to the original filename.

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);
}
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