fScan Reference Manual, Chapter 2 (CmdLineOptions:Expr): Roifill
usage: -expr roifill FILLVAL [ROINUM [NROIS]]
Fill region within selected Block ROI's. with FILLVAL If multiple Block ROI's are associated with the current data set, all will be filled by default. Or you can select just a subset of the active ROI's by specifying ROINUM (how many to skip) and/or NROIS (how many to use).