Step-by-step guide
You can use the grib_dump command with the "-D" option:
% grib_dump -D my.index
And the output will look something like this:
***** FILE: my.idx GRIB File: data/tigge_cf_ecmwf.grib2 GRIB File: data/tigge_af_ecmwf.grib2 Index keys: key name = mars.date values = 20070122, 20060630, 20060623, 20060811, 20060619 key name = mars.stream values = enfo, oper key name = mars.type values = cf, fc key name = mars.step values = 96, 0 key name = mars.param values = 228039, 228139, 133, 189, 168, 121, 122, 167, 147, 176, 177, 134, 146, 130, 228164, 136, 228228, 131, 132, 0 key name = mars.levtype values = sfc, pl, pv, pt key name = mars.levelist values = undef, 925, 2, 320 key name = mars.number values = 0, undef Index count = 8