PHP: Change a file name's extension for every file in an directory.

gistfile1.txt

function change_extension($filename, $index, $extension) {
  if (pathinfo($filename, PATHINFO_EXTENSION) == 'md'): 
    $fn = sprintf("%s.%s", pathinfo($filename, PATHINFO_FILENAME), (string)$extension);
    $success = rename(sprintf('./%s', $filename), $fn);
  endif;

  if($success) {
    printf("Success! %s was renamed to %s\n", $filename, $fn);
  }
}

// Sample usage
array_walk($files, 'change_extension','markdown');