Wouldn't the \\.\ cmd work? Or are the com ports in Linux different?
The syntax you provided is Windows centric in nature. As a general guide, backslashes (i.e. \ ) are for Windows, and forward slashes (i.e. / ) is for Linux. USB mining devices will usually show up as /dev/ttyUSB devices. My limited experience with bfgminer under Linux didn't include a specific device references, it just "found" them.
I didn have to build bfgminer at the time, and make sure to include the proper device support for the type of miner. I would almost certainly use cgminer now under Linux.