How do I chmod files in the following way?

Question

I have a directory with many subdirectories and files in it, and I would like to change the permissions of the files there the following ways. Basically, I want to protect the directories better.

First, all DIRECTORIES should be just chmod to 750 recursively, but only directories.

For files: if a file has a +x for the main user, it should be changed to 750, otherwise it should be changed to 640 (meaning no +x, r/w for the main user, r for the group, no permissions for world).

This should be applied to all files in all directories.

Is there a way to do that?

Answer 1

The X (capital X) mode character in chmod does the difficult bit: it lets you add execution permission only if it was already present for some user.

chmod -R g+rX-w,o= /path/to/directory

(Add user permission changes if desired.)

Answer 2

By "main user," I assume you mean the file owner? Find would probably work for you. Assuming /dir is the directory you're doing all this in:

# find /dir -type d -exec chmod 750 {} \;
# find /dir -type f -perm -u-x -exec chmod 640 {} \;
# find /dir -type f -perm -u+x -exec chmod 750 {} \;

The first one changes all directories to 750. The second one changes files without owner executable permission to 640. The third one changes the files with +x for the user to 750. These could probably be combined into a single find command but that would take a little more time to work out than I have to spend right now.