[gradsusr] Use wgrib2 to check if grib2 file is valid

[Ivan Toman]

Hello GrADS users,

Sometime when I download grib2 NCEP files with grib filter tool, I get 
incomplete file. How can I robustly use wgrib2 tool in bash script to 
check downloaded file if it is valid grib2 file or not?

Thank you!

Best regards,

Ivan Toman