You will need to open at least one file before you can enter other GrADS commands.
You open the data-descriptor file, not the raw data file (more on this later). The command is:
open filename
You can open more than one file. Each file is numbered in the order that you open it in. Initially, the "default file" is file 1, or the first file you open. The importance of the default file will be discussed later.
GrADS will read some GRIB data files directly, particularly those being produced by NMC. The GRIB records must contain lat-lon grids.
If you have GRIB data you would like to view, please contact doty@cola.umd.edu or fiorino@typhoon.llnl.gov.