It can be helpful to use Data::Dumper to visualise your data if you are not sure what is going wrong.

use strict;
use warnings;

use Data::Dumper;

my @arrA = ( [0, 1, 2] );
unshift @arrA, 1;

print Data::Dumper->Dump([\@arrA], [q{*arrA}]);

shift @arrA;
unshift @arrA, [1];

print Data::Dumper->Dump([\@arrA], [q{*arrA}]);
[download]

This code produces the following.

@arrA = (
          1,
          [
            0,
            1,
            2
          ]
        );
@arrA = (
          [
            1
          ],
          [
            0,
            1,
            2
          ]
        );
[download]

I hope this is useful.

Cheers,

JohnGG