I am not sure if this is the right place for this topic, but I am having trouble understanding the structure of a PDK...

I recently got a tsmc PDK that says in the manual to just untar both iPDK and DOC in the same place and run the pdkInstall.pl that goes through the details of setup...
What I don't understand from the little script is how can you effectively make a good hierarchy of different PDK setups without having to copy the original pristine PDK that you got.

If I didn't make myself clear, the point is that when I run the pdkInstall.pl I get to choose voltage scopes and metal schemes and etc., and you get to choose only one option of course, and then the script copies and removes the extras that weren't in your choice.
What I realised is that everything stays more or less the same in that folder in which I untarred the iPDK and DOC and ran the script...
so how do you know it's properly installed?
and how do you install the same PDK with different options without overwriting something and without having to copy the whole pristine_pdk?

---------------- another thing:

I ran into some old installation of a PDK from 2012, also from TSMC. In the ReleaseNote.txt of that oldie there was an instruction how to install the PDK that was different than the one I got now in 2016.
Says to make a directory where I wish to install my pdk, and then to untar the needed things from pristine_pdk to that new directory and then run it...
That makes a lot more sense, it's just that my new PDK seems confused about configuration variables and paths when I try it...
So I guess I am missing something...

Can anyone share their experience with installing PDKs?
I am, as you can guess, a total noob still, who knows a thing or two about shell scripting and unix...