Add som contours with the following commands.
First smooth the grid to achieve smooth contours:
decr4 -count 5 -in dtm_name.r4 -out temp.dec.r4
-count
it takes 5 pixels to create a single contour value.
Now make the contours:
contgrid temp.dec.r4 dtm_name.cont
You can view the result with:
jview dtm_name.8bit -vectbin dtm_name.cont
With the import command you can make an image of the dtm with contours, for example:
Get a example of a script
here. Remember, it may need some tweaking from yourself.