Accessing template variables after process

Hello,

is there a way to access the (modified) template variables from perl script after calling process? The reason I like to do that, is that I want to set the output filename from within the template file. Something like that: 

[% filename = "$somevar.$someextension" %]

From perl i like to read out the filename variable and save the instantiated template file under that name.

Any hints welcome!

Thanks in advance,

Daniel.