File Permission Inheritance?

If you are using Access Control Lists, note that the permissions are only inherited by items that are created in the folder, not moved there.

Normally you would create a copy and move that (option-drag), or create a new copy then remove the original.

Use Automator to create a Folder Action that changes the permissions when new files appear.

Use a run shell script, as the Automator task.

You could also Google "Mac Automator Folder Actions" for more examples.

From a terminal session issue the command

man chmod

and look at the acl's

And unless you are using an Account Server to provide use credentials, every user is local to the Mac. Someone accessing your Mac from a remote system will be mapped into a local account. When they create a file, just check to see what the ownership is, and use that in your acl settings.

Then add that chmod command to the Automator Folder Action.

Sorry, I do not have any personal magic for dynamically attaching a Folder Action to a newly created folder from an existing Folder Action. 😟

Maybe someone else has some ideas.

If time is not critical, AND the Folder tree is not HUGE, you could create something that wakes up every so often and just applies a

chmod -R ...your.stuff.here...

to just brute force the changes.

But if the interval was too frequent, or the size of the Folder tree was too big, you could be putting a lot of CPU and I/O load on your system that might interfere with normal operations.

I guess if you want to try and attach folder actions to new folders, you could figure out what kind of .plist is created and stored in what directory, then dynamically create a new plist and attach it using the launchctl command. Technically I think it could be done, but I have never tried it, so I don't know what the .plist would look like, nor where it would be stored, nor what the launchctl command to enable it would look like.

And if you are going down this path, you would have to keep in mind what happens when a given sub-folder was deleted. How do you clean up all the folder action scripts you created that no longer have a object to monitor?

But if you want to go down this path, then warm up your "Google Foo" and start researching.

As mentioned it can get a bit unwieldy if you have a lot of folders, but System Events has some (hidden for whatever reason) commands for folder actions:

tell application "System Events"
  attach action to attachedFolderAlias using folderActionScriptAlias
  remove action from attachedFolderAlias using action name nameOfFolderActionScript
end tell