#!/usr/bin/env perl

use strict;
use warnings;
use 5.010;

use lib '.';
use MyModule;

my_sub;

say "Main program: $var";

##</code><code>##

package MyModule;

use strict;
use warnings;
use 5.010;

use base 'Exporter';

our $var;

our @EXPORT = qw( my_sub $var );

sub my_sub {
  $var = 42;

  say "Set \$var to $var in my_sub";
}

##</code><code>##

$ ./prog.pl 
Set $var to 42 in my_sub
Main program: 42