r.reclass lets you aggregate raster classes, which is useful for extracting out one or two classes of interest and lumping all other classes into a single "other" category. It does not actually create a new raster map, only a reclass file in the cellhd directory of your mapset referencing an existing map.
You can run r.reclass interactively, entering successive reclass rules at the reclass prompt. The general format of a reclass rule is oldval(s) = newval [label]. Examples:
2 = 1 3 4 5 = 2 forest 5 thru 10 = 3 coniferous forest 8 thru 12 16 thru 22 = 4
To resolve inconsistencies (such as the above) succeeding rules overrule prior rules.
When entering reclass rules interactively, terminate rule entry with "end."
It is often easier to re-direct reclass rules from a text file:
r.reclass i=elevation.dem o=elev.reclass < elev.recl.rules
If you g.remove the original map on which a reclass map is based, you will lose the reclass map as well. If you want to create a separate raster file for a reclass map, run r.mapcalc perm.map=reclass.map (see r.mapcalc).