in reply to Can you import ENV variables at run time?
There are a few you could guess at from the contents of the passwd file: home directory, initial shell; but past this it's going to be hard to guess what the environment variable would have been.
If you run your scripts using the shell (after setting $HOME, $USER, etc.) you may be able to get the shell to interpret these files. For instance, under bash you can do this:
and get the environment variables set.system("/bin/bash --login -c $yourScript");
update: I realize that not everyone has the same shell; you'd want to use getpwuid to get the passwd file setting for login shell and HOME. tilly's suggestion sounds good.