Define a package:

package Pack;
my $foo = 'pack';

sub import {
    my $pkg = caller();
    no strict 'refs';
    *{ $caller . '::foo' } = \$foo;
}

1;
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Now write a program:

#!/usr/bin/perl -w

use strict;
use Pack;

print "$foo\n";
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After realizing that names have scope, variables do not (Dominus once said something similar), print out this page. Then eat it. :) ©