You can add --form mediaFiles=@<local_path>
. If you have more than one media attachment, you can just keep adding more of those. For example:
curl --verbose --digest --header "Content-Type: multipart/form-data"
--form form_def_file=@/Users/form1.xml
--form mediaFiles=@/Users/data.csv
--form mediaFiles=@/Users/image1.jpg
--form mediaFiles=@/Users/image2.jpg
https://xxxx.appspot.com/formUpload
You can see the receiving code here.