#!/usr/bin/perl -w
#use forking open to start 3 more processes

unless (open X, "-|") { print 1+5;     exit }; # X=1+5
unless (open Y, "-|") { print 2*3;     exit }; # Y=2*3
unless (open Z, "-|") { print <X>+<Y>; exit }; # Z=X+Y

print "Z = "; print <Z>."\n";