use Data::Dumper;
use strict;
use warnings;

my $a = ["abc","cba"];
if (defined($a->[2]) && $a->[2] ne '') {
}
print Dumper($a);
if (defined($a->[2]->[3]) && $a->[2]->[3] ne '') {#this is autovivification
}
print Dumper($a);

##</code><code>##

$VAR1 = [
          'abc',
          'cba'
        ];
$VAR1 = [
          'abc',
          'cba',
          []   #this is autovivification
        ];