What is the equal of ArcGIS Raster calculator "Mod" function (Finds the remainder of the first raster when divided by the second raster on a cell-by-cell basis.) in r. mapcalc in GRASS GIS?
There is no function, but you can use the modulus operator, which is "%" in GRASS (as in many other languages), e.g. 8%5=3
for a pixel-by-pixel computation, simply use the layer names