In Perl, how can I access a scalar defined in another package?

Question

I seem to be stuck trying to access a scalar which is defined in another package, and have narrowed down an example to a simple test case where I can reproduce the issue. What I wish to be able to do it access a reference to a list which is in defined within the package 'Example', using the our mechanism, however, Dumper is showing that the variable is always undefined within example.pl:

Example.pm looks like the following:

#!/usr/bin/perl -w

use strict;
use warnings;
use diagnostics;

package Example;
use Data::Dumper;

my $exported_array = [ 'one', 'two', 'three' ];
print Dumper $exported_array;

1;

And the code which uses this package looks like this:

#!/usr/bin/perl -w

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

use lib '.';
use Example;

{ package Example;
  use Data::Dumper;
  our $exported_array;
  print Dumper $exported_array;
}

exit 0;

Upon running this code, the first Dumper runs and things look normal, after this, the second Dumper, example.pl runs and the reference is then undefined:

$VAR1 = [
          'one',
          'two',
          'three'
        ];
$VAR1 = undef;

Answer 1

A my declaration does not create a package level variable and does not enter anything onto the symbol table for any namespace.

To do what you look like you are trying to do, you will have to change the declaration in the first file to

our $exported_array = [ ... ];

You can then access it in another file as

$Example::exported_array

Answer 2

Even if $exported_array weren't lexically scoped in the Example package, Example's $exported_array and main's $exported_array are two different things. The easiest way to change the example you've given is to 1. change my to our in the Example declaration and explicitly qualify the variable name.

our $exported_array;

...

print Dumper $Example::exported_array;

Otherwise, you need to make Example an Exporter. (Or just write an Example::import routine--but I' not going to cover that.)

package Example;
our $exported_array = ...;
our @EXPORT_OK = qw<$exported_array>;
use parent qw<Exporter>;

And in the script:

use Example qw<$exported_array>;

However, as you can actually export arrays (not just refs), I would make that:

our @exported_array = (...);
our @EXPORT_OK      = qw<@exported_array>;
...
use Example qw<@exported_array>;
...
print Dumper( \@exported_array );