question for gridmap

[wenting]

Hi, dear Grads users:
    I installed grads-1.8sl11-win32e.exe. I tried to use 'gribmap' to
generate *.idx by
$gribmap -i grib_file.ctl -0 or
$gribmap -i grib_file.ctl

But both of them do not work. How can I get *.idx ?

Thanks for your kind help!

Best wishes,
Wenting