[wix-users] How to pass the INSTALLFOLDER used to a program run as a custom action

[Angus Comber]

I run a program, config_maker.exe, at the end of install but I need to know
the installation folder to write data to.

When I run the installer the current directory seems to
be C:\Windows\system32 , so I need to pass the instal path to the program.
I can do this on the command line.  What syntax to use?

Here is my custom action:

    <CustomAction Id="EXECUTE_AFTER_FINALIZE"
              Execute="immediate"
              Impersonate="yes"
              Return="asyncNoWait"
              FileKey="config_maker.exe"
              ExeCommand="INSTALLFOLDER" />

I have a DirectoryRef for install folder like this:

    <DirectoryRef Id="INSTALLFOLDER">

I get config_maker.exe print output to a known place and the argument is
printed like this:

arg=INSTALLFOLDER

So do I pass in a variable that will get substituted with the real value on
install?