So you want the behavior of a global variable without a global variable? Are you trying to limit access to the value, or are you just trying to create persistent parameters? In either case, sounds like you want to go OOP-esque.

package Parameters;
use strict;

use Exporter;
our @ISA = qw(Exporter);
our @EXPORT = qw(get_var);
my $var = "xpto";

sub get_var{
    return $var;
}

1;
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and then call it as

use Parameters;

print get_var;
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This has the added benefit that $var is completely inaccessible outside of any accessor methods you give the user.