package Thingy;

sub new {
   my ($class, $line) = @_;
   my $thingy = {}; 
   ...
   if ($line =~ m/$PATTERN/) {
      ...
   }
   bless $thingy, $class;
}
1;

##</code><code>##

package Rubber;
@ISA = qw(Thingy);
use vars $PATTERN = q(...);
1;

##</code><code>##

use Rubber;
my $line = ...;
my $thing = Rubber->new($line);