I’m running up2date ownyourbits ncp image as a docker container on rpi4 with dietpi as base system.
Besides I have another container running doing some bash scripts for me to create certain files on daily base.
In the past I uploaded these files that are stored on external USB drive with the Dropbox Uploader Script to my Dropbox or accessed them through ssh/ftp.
Now I want to be more independent with nextcloud and thought I easily can use a simple cp command to copy the files to my nextcloud location. 
Nextcloud is up and running but what would be the best way to copy these files, stored on USB drive, within a shell script to its nextcloud database destination?
Do I have to use ssh/ftp/scp or is there even a “networkless” way?
This nextcloud is volumed to the external USB drive as well but that wouldn’t make a big difference in my use case I think 
Search “nextcloudcmd”.
Thx @devnull that pointed me to right direction.
Today I ftp’ed a bit and found “/mnt/volumeonext/nextcloud/data/user/files”
So both methods copy directly with cp or ftp and with docker cp from host to container should work.
But now my problem is that Nextcloud frontend won’t recognize the changes I made manually. It still shows the original file structure but “ls /data” inside the container shows me that the changes I made are correct. So why isn’t Nextcloud WebUI self updating?
Edit:
files:rescan is my friend
I can do it with “docker exec -it containername /bin/bash”
and then “sudo -u www-data php /data/nextcloud/occ files:scan --all”
BTW how can I figure out the UID from my user?
The above does it well but I need it executed from inside a bash script…
You find it in /etc/passwd
Or
id
id username
@devnull
So you mean the system uid? I need the uid from nextcloud user to avoid scanning --all when refreshing 
Im not planning to have so many users but is still interesting to know where to find it. --plainusername wont work for rescanning.
Also Im stuck in trail and error mode for finding a simple one liner to run rescan command from script at host.
But as Im writing this I think of having 2 scripts. 1 at host that triggers a script inside container and inside container for the rescan
Really? I have never test it.
docker exec --user www-data <containername> php occ files:scan --all
the help text is misleading. it should be user_name instead of user_id.
docker exec --user www-data <containername> php occ files:scan diggidre
thx @Reiner_Nippes
I thought it hast to be --usrname but without the – did it 
But the above 1 liner wont work. No matter if I use container name or hash / id it tells me file or folder not found… and without containername in <> i get “Could not open input file: occ”
this is non-default path. maybe you have to add it.
docker exec --user www-data <containername> php /data/nextcloud/occ files:scan --all
why did you change the path?
@Reiner_Nippes
Ahh the path to occ is not standard… I don’t know why it’s different. Im using official NextcloudPi Image.
Solved