expanding an environment variable

[Mike Linacre]

Folks:
An end-user wants to run a silent install with a batch-file command similar to:
softwareinstall.exe "/S:XXXsetupvars.ini"
where XXX is a Windows environment variable with value: c:\my folder\my subfolder\

How can I expand the environment variable in the Setup Factory install so that
XXXsetupvars.ini
becomes
c:\my folder\my subfolder\setupvars.ini

Any ideas?

Later: solved!
softwareinstall.exe "/S:%XXX%setupvars.ini"