A hash or array element can be true only if it's defined and defined only if it exists, but the reverse doesn't necessarily hold true.

##</code><code>##

exists may also be called on array elements, but its behavior is much less obvious and is strongly tied to the use of delete on arrays.

WARNING: Calling exists on array values is strongly discouraged. The notion of deleting or checking the existence of Perl array elements is not conceptually coherent, and can lead to surprising behavior.

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my @array;
$array[3] = 2;
print Dumper \@array;

__END__

$ perl test.pl 
$VAR1 = [
          undef,
          undef,
          undef,
          2
        ];