my ($x, $y, $z) = ('', '', '');
($x, $y, $z) = split(',', $_);

##</code><code>##

my ($x, $y, $z) = map { $_ || '' } split(',', $_);

##</code><code>##

use strict;
use warnings;

$_ = "a,0,b";
my ($x, $y, $z) = split(',', $_);
foreach ($x, $y, $z) { $_ = '' unless defined($_) }

print "x = $x\ny = $y\nz = $z\n";

__END__

x = a
y = 0
z = b