package A;
use strict;
BEGIN {
  use Exporter();
  use vars qw(@EXPORT @ISA);
  @EXPORT = qw($var1);
  @ISA = qw(Exporter);
}
use vars @EXPORT;
$var1 = "1";

##</code><code>##

#!/usr/bin/perl
package B;
use strict;
use A;
print "$var1\n";

##</code><code>##

package A;
...

##</code><code>##

...
use A1;
...