Hi, welle,
From your OP, I would assume you want variable file names. If you want to have variable file contents (without the need of disk I/O), the possibility depends on the external program. If it can use STDIN/STDOUT, then you should probably look into IPC::Open2.
Yes, I ment to pass the content of a variable to the .exe and get the result of the .exe operation in another variable. I'll have a look at what you said.