($x, $ENV{Z1Z1}) = ( '3', '2,1' );  # first time
  ($x, $ENV{Z1Z1}) = ( '2', '1' );  # second time
  ($x, $ENV{Z1Z1}) = ( '1', undef );  # third time

##</code><code>##

  my @arr = split /,/, $ENV{'Z' . uc $foo}, 2;
  $x = shift @arr;
  $ENV{'Z' . uc $foo} = scalar @arr ? $arr[0] : '';   # set to empty string if nothing available