NextCloud Files_Anti-Virus Simple Install
Make sure ClamAV is installed and running on your server.
Move to the apps directory in your NextCloud installation
’cd [path to nextcloud]/apps`
Download the app from GitHub. Use:
https://github.com/nextcloud/files_antivirus/archive/stable10.zip for Nextcloud 10
https://github.com/nextcloud/files_antivirus/archive/old-master.zip for version 11
https://github.com/nextcloud/files_antivirus/archive/stable12.zip for Nextcloud 12
https://github.com/nextcloud/files_antivirus/archive/master.zip for Nextcloud 13
[sudo] wget https://[link to the version you need]
Unzip the file into your nextcloud/apps directory.
Chown that folder to your web server user (www-data in my case). (Not sure this is necessary but it keeps things tidy.)
[sudo] chown -R www-data:www-data files_antivirus-master
Rename the directory
[sudo] mv files_antivirus-master files_antivirus
(Not sure if this is actually necessary, but I reloaded my apache vhosts here.)
[sudo] service apache2 reload
Log on to NextCloud and goto Apps. In the “Not enabled” section, enable “Antivirus App for files”
Move to the admin section and setup as necessary.
edit: updated links in body