How do I set a variable on a pipe ????

This I suspect is more a question of Unix in general than procmail, but here
goes .. 

How do I set a variable (say ADDRESS) equal to the output of a command,
when the input to the command is on the standard input with a pipe ? 

For example, if a prcomail rule is:

:0
| ($FORMAIL -x "From:" ) | $GREP -f $HOME/white.list


how can I set a variable equal to the output from that command string ??


Trying to say 
ADDRESS = | ($FORMAIL -x "From:" ) | $GREP -f $HOME/white.list

just does not work, whereas it would if the command did not start at the 
standard input. 

dave kirby
_______________________________________________
procmail mailing list
procmail(_at_)lists(_dot_)RWTH-Aachen(_dot_)DE
http://MailMan.RWTH-Aachen.DE/mailman/listinfo/procmail