Step-by-step guide
For example using grib_get, you may want to show all messages which have a level of 100, 150 or 200. The way to do this is to use the "/" (forward slash) character in the "where" clause (for the -w switch)
% grib_get -w level=100/150/200 ...
This can be combined with an "AND" condition (logical conjunction). So if I want to show all messages whose level is either 0 or 1 and whose type is "an":
% grib_ls -w level=0/1,dataType=an ...
This would be equivalent to the pseudo-code:
if (dataType == "an" AND (level == 0 OR level == 1)) ...
Note: To have even more control over selecting messages, you can use the grib_filter tool.