selective archive listing?

Hi. I have a number of rar archives, and I want to get a list of the contents and pipe it to a file. But I only care about directories/folders, not the files that they contain.

I've tried using "unrar lb file.rar >> output.txt" but this lists all files.
"unrar vb file.rar >> output.txt" is better - it gives me the folders, but also all the files.

Is there any way to achieve what I want using winrar or any utility in the rar toolbox?

thanks,
CT.