[SVRF] setting window size of "DENSITY" function using environment variables

Is it possible to set the size of window in "DENSITY" function using environment variable?

I know that I can do it as follows:

export env_var1=10 (in a shell)

#IFDEF $env_var1 10

     #DEFINE env_var1 10

#ELSE

     #IFDEF $env_var1 20

               #DEFINE env_var1 20

     #ELSE

          #IFDEF ...

I wonder whether I can directly set the size of window using an environment variable without writing multiple if-else clauses.