How to change a parent shell's environment? putenv would not.

[George A. Planansky]

I want to run two programs, minmax and plot, thusly:

    minmax < 2D-data | plot > lpr

such that minmax sets the environmental variables DMIN and DMAX, which are
read by plot before it takes action.

I can use putenv and getenv to change the set of environmental variables
seen by minmax, but this does not change the environment that plot sees.  

1) how can I get minmax to change the variables that plot will see?
2) need I do something to ensure that plot does not start filtering
   the data stream BEFORE minmax has updated the variables?

I'd like to use the environment to pass these values, because it would be
easy to get the values.  If this "can't be done", is there some other
"easy" way?  I'd like to avoid using files, but if this is the way to go,
I shall.

Please mail replies to:  gplan at ra.umb.edu .  Thanks.

George Planansky (617) 547-6207
Atmosphere Environment Research, Cambridge MA