4.3BSD/usr/contrib/icon/book/07/exor1.icn

procedure exor(s1,s2)
   local count, line
   count := 0
   while line := read() do
      if find(s1,line) then {
         if not find(s2,line) then count +:= 1
         }
      else if find(s2,line) then count +:= 1
   return count
end