"It is usually a good idea to put "global variables" into a Common module of some kind, perhaps which exposes an object that simply serves as the repository of those values."

Do you mean explicit package + object oriented?

I already use a separate perl module and I'm thinking using explicit package name in addition. But I don't want to put object oriented programming with the rest of the code, which is not.

But I fully agree with you that explicit package name is a better practice (even for small projects like mine, it doesn't hurt).

And yes I already put use strict and use warnings everywhere :D

Then you could use a pseudo-object, for example storing your global variables in a lexical hashref in the const module, and have in that same module a get and a set functions to access the hash that you export. Something like this:

use strict;
use warnings;
use Exporter;

our @ISA = 'Exporter';
our @EXPORT = qw(get set);

my $private_hash_ref = {VAR1 => "one", VAR2 => "two"};

sub get { my $key = shift; return $private_hash_ref->{$key};}
sub set { my ($key, $value) = @_; $private_hash_ref->{$key} = $value;}
[download]

And then in your main code or other module, you just use the set and get functions.