Question: I want a command to shred completely the contents of a folder/directory (which may be inside folders/directories).
Also please explain the command.

Answer: 
`sudo apt install wipe`

`$ wipe -rfi dir/*`

where the flags used:
`-r – tells wipe to recurse into subdirectories
-f – enables forced deletion and disable confirmation query
-i – shows progress of deletion process`
You probably want to use something similar to this:

```
find dir -type f -exec shred -fuz {} +
rm -rf dir

```

First command finds only files and passes them to shred (as many at once as possible - no need to start a new shred process for every file like \; does). Finally, remove the directories too.