Shell command line that is called before encrypting and saving a file after upload. Before calling, the path to the uploaded file and the output diversion '2>&1' are added. This option can be used to hook up a virus scanner. If the parameter is empty, no pre-processing takes place. The result code of the shell process is checked. If it is not 0, the uploaded file is deleted and the uploader gets an error message depending of the active language.