I like to backup my ownCloud calendars and addressbooks as .ics/.vcf files, because it is very easy to restore: just import the backed up .ics/.vcf file to the server or a client and the accidentally deleted data is back online.
Therefore I initially wrote a bash script with hardcoded links for my installation. Two friends were interested and so I improved the script to be more generic which possibly makes it interesting for other users as well.
The script downloads all available calendars/addressbooks belonging to certain users from a ownCloud instance as .ics/.vcf files. Usernames and according passwords have to be given in a separate file. All downloaded files are then compressed to a single file with the current date in the filename.
It works with all ownCloud versions >= 5.0 (and Nextcloud as well) and has been tested under Debian Wheezy and Jessie. Of course shell access to the server is needed. Configuration is quite simple: in most cases the path to the ownCloud directory sufficient. It is not necessary to run the script with root privileges - in default configuration it only needs to have read access to ownClouds configuration file 'config.php'. At no point any data leaves the server.
If that sounds interesting to you, you are welcome to use it: