[nmglug] chmod question

[Andres Paglayan]

I have a big tree of directories generated by a php script, it goes from 
a/ to z/ and it has a/ to z/ within each one.
I backuped and restore it (after changing the OS from Fedora to Debian)
I want to change the permissions only in the directories without 
affecting those of the files.
Is there any way to do that recursively on the dirs but skiping the files?
thanks,
Andres