Only works with Akeeba Backup Professional.
What it does: Add an additional off-site directory to be backed up by Akeeba Backup.
Syntax: akeeba:filter:include-directory DIRECTORY [--profile=PROFILE] [--virtual=VIRTUAL]
Arguments
This command takes one mandatory argument.
The absolute path to the off-site directory (folder) you want to include in the backup.
Options
Optional. The backup profile to use. Default: 1.
Keep in mind that filters are set per backup profile. They are not reused across backup profiles.
Optional. The subfolder inside the backup archive where these files will be stored.
All off-site folders are backed up inside the backup                  archive as a subdirectory inside a folder called                  "external_files" (the name of this folder can be configured                  in the Configuration page of the backup profile). So, if you                  were to enter example here, the contents of                  the directory would be backed up inside the backup archive                  under the path                  external_files/example.
If you do not specify this option the name of the virtual folder will be determined automatically.
Exit codes
One of the following exit codes will be set when the command finishes running:
The command completed without an error.
You have Akeeba Backup Core. This feature is only available in Akeeba Backup Professional.
A folder inclusion filter with the same connection information already exists.
Setting the filter failed.