[GRASSLIST:4028] Re: GRASS4.3 mapcalc

[Soil & Water Lab.]

Hi,
This topic is referenced in the help manual, r.mapcalc entry...

"Extra care must be taken if the expression is given on the command line. Some 
characters have special meaning to the UNIX shell. These include, among 
others: 
* ( ) > & | 
It is advisable to put single quotes around the expression; e.g.: 
        result = 'elevation * 2'
 Without the quotes, the *, which has special meaning to the UNIX shell, would 
be altered and r.mapcalc would see something other than the *. "

That's the main trick : it seems that you forgot the single quote.
Basically, always use quotes.

A nice trick with scripts : if you want to refer to maps by using variable 
names, you may prefer the syntax 

echo "your formula" | r.mapcalc

echo "newmap=$oldmapname*2." | r.mapcalc

example 
fieldmap= fields2
randrast=randrast2
echo "randfood=$fieldmap*$randrast" | r.mapcalc


-- 
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Soil and Water Laboratory
Biological and Environmental Engineering Department
Cornell University
Riley-Robb Hall
ITHACA, NY 14853 - USA