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Is it possible to whitelist specific file extensions for folders?

For example: I would like to move music albums to a folder, but I don't want the cover art to be transferred by disallowing *.png, *.jpg, etc.,...

You can either do the filtering on copying, say, in the copy script. Or you can apply the filter after the copy operation, removing what's not allowed or needed.

The question is certainly broader than the issue so the answer may vary.

Originally, Unix-like systems do not know the concept of file extension although some software may identify extensions to adapt their operations.

Moreover, a pathname expansion must match existing files or directories located on a specified level in the file system (hierarchical filesystem).

mv can move an entire directory hierarchy, therefore, mv also moves files located in matching directories, indistinctly.

A simple solution is to remove the read permission on the wanted files to prevent them to be copied.

prompt% cp -vr album /tmp
'album/' -> '/tmp/album'
'album/song.mp3' -> '/tmp/album/song.mp3'
'album/covert.png' -> '/tmp/album/covert.png'
 cp: cannot open 'album/covert.png' for reading: Permission denied
prompt% ls -l album/covert.png
--w-r--r-- user user 8 Sep 07:27 album/covert.png 

Files are transferred in the target directory except files that are protected for reading.

The naive way to solve this is to copy everything and then to delete the file you don't want.

Using rsync to copy the whole source directory structure to target, then find to delete the files you don't want from target:

rsync -a source/ target

find target -type f ( -name '*.jpg' -o -name '*.png' ) -delete

A more streamlined way to do this is to use the filtering capabilities of rsync to not transfer the files you don't want:

rsync -a --exclude='*.png' --exclude='*.jpg' source/ target

In both of these cases, you might possibly want to add --delete and/or --delete-excluded to the rsync invocation if you want to delete files not present in the source directory (if target already contains stuff and you want the two directories to be identical apart from those image files).