Better Upload Filename Sanitization in WordPress

October 28th, 2015

If you are like me, you feel like there is a lot to be desired for how uploaded filenames look in WordPress. Don’t get me wrong, it does a decent job in terms of making them web-safe (sometimes?), but for actually making a standardized, consistent structure across everything – not so much. Here’s something I’ve been throwing in my theme’s functions.php as of late. Written to be easily editable.

// Sanitize file upload filenames
function sanitize_file_name_chars($filename) {

  $sanitized_filename = remove_accents($filename); // Convert to ASCII

  // Standard replacements
  $invalid = array(
    ' ' => '-',
    '%20' => '-',
    '_' => '-'
  );
  $sanitized_filename = str_replace(array_keys($invalid), array_values($invalid), $sanitized_filename);

  $sanitized_filename = preg_replace('/[^A-Za-z0-9-\. ]/', '', $sanitized_filename); // Remove all non-alphanumeric except .
  $sanitized_filename = preg_replace('/\.(?=.*\.)/', '', $sanitized_filename); // Remove all but last .
  $sanitized_filename = preg_replace('/-+/', '-', $sanitized_filename); // Replace any more than one - in a row
  $sanitized_filename = str_replace('-.', '.', $sanitized_filename); // Remove last - if at the end
  $sanitized_filename = strtolower($sanitized_filename); // Lowercase

  return $sanitized_filename;
}

add_filter('sanitize_file_name', 'sanitize_file_name_chars', 10);

File: ~Super Important Document~.pdf
Default WordPress: Super-Important-Document.pdf
Custom Solution: super-important-document.pdf

File: ÐÕçument full of $$$.pdf
Default WordPress: ÐÕçument-full-of-.pdf
Custom Solution: document-full-of.pdf

File: Really%20Ugly%20Filename-_-That_-_Is_Too Common…..png
Default WordPress: Really-Ugly-Filename-_-That_-_Is_Too-Common…..png
Custom Solution: really-ugly-filename-that-is-too-common.png