I'm writing a freeware version of an app and would like to check if a user already has the unfree version installed, and print a message whose contents are conditional on the results of the installation check... anybody know if this is possible?

the closest I've come to a solution is to make use of the CFPreferencesSetValue API with a kCFPreferencesAnyUser / kCFPreferencesCurrentHost pairing... I haven't tried it, but based on the documentation it sounds possible.

however in my current specific situation this API will not be able to solve my problem, because I want to check for the presence of an app I wrote 4 months ago that didn't write any data to the CFPrefs registry... because back then I didn't know of it nor did I foresee this situation arising... the only way CFPrefs can assist me is in future apps now that I know it exists :)

so I'm wondering if there are other ways to do it? any help will be appreciated :)