# package to group all constant, read-only vars like $DEBUG
# file is Constants.pm and can be placed in same dir as main script
# or in a './lib' dir, make sure to adjust 'use lib...' in any subscript it uses it
package Constants;

use strict;
use warnings;

# boilerplate
use Exporter;
our @ISA = qw/Exporter/;

# add here all the variables you want exported
our @EXPORT = qw/$CON1 $CON2 $DEBUG/;

our $CON1 = 'a constant';
our $CON2 = 'another constant';
our $DEBUG = 1;
1;