       lvarpush var string ?indexExpr?
              The  lvarpush  command  pushes (inserts) string as an element in
              the list contained in the variable var.  The element is inserted
              before position indexExpr in the list. If index is omitted, then
              0 is assumed.  If var does not exists, it is created.

              If the expression indexExpr starts with the string end, then end
              is  replaced with the index of the last element in the list.  If
              the expression starts with len, then len is  replaced  with  the
              length  of  the  list.  Note the a value of end means insert the
              string before the last element.
