For those interested ... I have updated the library to include a feature called 'prefabs' - prefabricated command structures and handlers. The first prefab is for file navigation and manipulation and allows you to navigate SD card file structures, read, write and delete files and directories.
Writing to files is best done with something other than the Arduino serial port because to terminate a file write you need to send the ASCII value 4. On some terminal apps this can be done with CONTROL+D, but not with Arduino.
Also added since my first post is a locking system so you can impliment passwords. Locks can be hard or soft. Soft locks still permit internal commands such as help. Hard locks block all commands except the unlock command.