use also calls a class method called import every time it's encountered. You can use Exporter to make variables and functions available to other packages, or you can write your own import routine. I suggest the former.

package My::Constants;
use vars qw( $x $y @EXPORT_OK @ISA );
use strict;
use Exporter ();

@EXPORT_OK = '$x';
@ISA       = 'Exporter';

$x = 'my constant x is a lovable fellow';
$y = 'his ears are green and his belly is yellow';

1;
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It occurs to me that that's a lot of setup code. There's room for a nicer version of Exporter.