Automator chmod permissions help

[drjustice]

Hi, I've created an automator workflow to propagate permissions on a directory however i'm having some trouble over writing existing permissions.

This is the script;

chmod -R +a "<jsmith> allow read,write,delete" "/Users/xxxx/Documents/Permissions Test"

If I check the permissions in finder before I run the above script I see the following;

Name Privilege
<jsmith> Read

Once i've run the script I see;

Name Privilege
<jsmith> Custom
<jsmith> Read

I don't want to add another entry I just want to update the permissions to Read & Write

Any help would be appreciated.