Perl Importing Variables From Calling Module - perl

Question

I have a Perl module (Module.pm) that initializes a number of variables, some of which I'd like to import ($VAR2, $VAR3) into additional submodules that it might load during execution.
The way I'm currently setting up Module.pm is as follows:
package Module;
use warnings;
use strict;
use vars qw($SUBMODULES $VAR1 $VAR2 $VAR3);
require Exporter;
our #ISA = qw(Exporter);
our #EXPORT = qw($VAR2 $VAR3);
sub new {
my ($package) = #_;
my $self = {};
bless ($self, $package);
return $self;
}
sub SubModules1 {
my $self = shift;
if($SUBMODULES->{'1'}) { return $SUBMODULES->{'1'}; }
# Load & cache submodule
require Module::SubModule1;
$SUBMODULES->{'1'} = Module::SubModule1->new(#_);
return $SUBMODULES->{'1'};
}
sub SubModules2 {
my $self = shift;
if($SUBMODULES->{'2'}) { return $SUBMODULES->{'2'}; }
# Load & cache submodule
require Module::SubModule2;
$SUBMODULES->{'2'} = Module::SubModule2->new(#_);
return $SUBMODULES->{'2'};
}
Each submodule is structured as follows:
package Module::SubModule1;
use warnings;
use strict;
use Carp;
use vars qw();
sub new {
my ($package) = #_;
my $self = {};
bless ($self, $package);
return $self;
}
I want to be able to import the $VAR2 and $VAR3 variables into each of the submodules without having to reference them as $Module::VAR2 and $Module::VAR3. I noticed that the calling script is able to access both the variables that I have exported in Module.pm in the desired fashion but SubModule1.pm and SubModule2.pm still have to reference the variables as being from Module.pm.
I tried updating each submodule as follows which unfortunately didn't work I was hoping:
package Module::SubModule1;
use warnings;
use strict;
use Carp;
use vars qw($VAR2 $VAR3);
sub new {
my ($package) = #_;
my $self = {};
bless ($self, $package);
$VAR2 = $Module::VAR2;
$VAR3 = $Module::VAR3;
return $self;
}
Please let me know how I can successfully export $VAR2 and $VAR3 from Module.pm into each Submodule. Thanks in advance for your help!

Answer 1

In your submodules, are you forgetting to say
use Module;
? Calling use Module from another package (say Module::Submodule9) will try to run the Module::import method. Since you don't have that method, it will call the Exporter::import method, and that is where the magic that exports Module's variables into the Module::Submodule9 namespace will happen.
In your program there is only one Module namespace and only one instance of the (global) variable $Module::VAR2. Exporting creates aliases to this variable in other namespaces, so the same variable can be accessed in different ways. Try this in a separate script:
package Whatever;
use Module;
use strict;
use vars qw($VAR2);
$Module::VAR2 = 5;
print $Whatever::VAR2; # should be 5.
$VAR2 = 14; # same as $Whatever::VAR2 = 14
print $Module::VAR2; # should be 14

Answer 2

Well there is the easy way:
In M.pm:
package M;
use strict;
use warnings;
#our is better than "use vars" for creating package variables
#it creates an alias to $M::foo named $foo in the current lexical scope
our $foo = 5;
sub inM { print "$foo\n" }
1;
In M/S.pm
package M;
#creates an alias to $M::foo that will last for the entire scope,
#in this case the entire file
our $foo;
package M::S;
use strict;
use warnings;
sub inMS { print "$foo\n" }
1;
In the script:
#!/usr/bin/perl
use strict;
use warnings;
use M;
use M::S;
M::inM();
M::S::inMS();
But I would advise against this. Global variables are not a good practice, and sharing global variables between modules is even worse.