Arrays and negative indexes in Perl

Question

I am newbie in Perl and I am reading about arrays.
As I understand the arrays expand automatically as needed (cool!)
But I also read that we can use neg

Answer 1

You get an undef value if You read the value.

use strict;
use warnings;

my @l = qw(A B C);
print $l[-4];

Output to stderr (program continues to run):

Use of uninitialized value in print at ./x.pl line 7.

Or:

my @l = qw(A B C);
print "undef" if !defined $l[-4];

Output:

undef

If You want to assign a value to it You get an error:

my @l = qw(A B C);
$l[-4] = "d";

Output (program exits):

Modification of non-creatable array value attempted, subscript -4 at ./x.pl line 7.

And actually the interval can be modified. So an array can start any value not only 0.

my @l = qw(A B C);
$[ = -4; # !!! Deprecated
print $l[-4], "\n";
print $l[-3], "\n";

Output:

A
B