Exporting dxf with elevation?

[Andreas Bullinger]

 I'm trying to export a contour map from Grass to Autocad (12/14). I made
a contour map with r.contour, transformed the binary vector to ascii and 
exported to dxf with v.out.dxf. The polylines are ok, but they have the
elevation zero. 

In the WEB I found the hint:

sort +3n -4 in_file > in_file.sort  
join -j1 4 -j2 1 -o 1.1 .1.2 1.3 2.1 in_file.sort file2 > file.join 
#in_file is a dig_att file that must be sorted for join to work
#file.join will be th new dig_att file to trick GRASS into providing dxf
files with actural polygon labels . Rename corresponding GRASSfiles to 
match file.join

The sort command seems to work. Does anyone know what file2 should be?
What corresponding GRASSfiles have to be renamed?

Does anyone know a module for Grass exporting dxf Files with elevation?

Thanks
Andreas Bullinger