@bar = (1,2,3) unless @bar;

##</code><code>##

$bar ||= (1,2,'x');
print $bar, "\n";

##</code><code>##

my ($a, $b);
($a, $b) ||= ('a', 'b', 'c'); # $a unchanged, $b <- 'c'
($a, $b) ||= (1, 2, 3); # $a unchanged, $b unchanged
$b = (1, 2, 'x'); # $b <- 'x'
$a ||= (3, 4, 5); # $a <- 5

##</code><code>##

($a, $b) = (7,8,9); # $a <- 7, $b <- 8