how does grep work inside a docker container?

Well, for any potential future readers, I had no luck getting grep to do it, I’m sure it was my fault somehow and not grep’s, but thanks to the help in this post I was able to use awk instead of grep, like so:

docker exec -it 1c8c05daba19 awk '/^\$OC_VersionString/ && match($0,/\047[0-9]+\.[0-9]+\.[0-9]+\047/){print substr($0,RSTART+1,RLENGTH-2)}' /config/www/nextcloud/version.php

That ended up doing exactly what I needed:

• It logs into a docker container.
• Scans and returns just the version number from the line I am looking for at: /config/www/nextcloud/version.php inside the container.
• Exits stage left from the container with just the info I needed.
• I can get right back to eating my Hot Cheetos.