use strict;
use warnings;

my $foo = '1Z1';
$ENV{Z1Z1} = '3,2,1';

for (1..5)
{
    my $x = '?';
    if ($ENV{'Z' . uc $foo})
    {
        ($x, $ENV{'Z' . uc $foo}) = split /,/, $ENV{'Z' . uc $foo}, 2;
    }
    print $x, $/;
}