You are passing an argument to the new method, but not using it... Try

package shapes;

#constructor
sub new {
    my ($invocant, %hash) = @_;    
    my $class   = ref($invocant) || $invocant;

    my $self = {
        shape  => $hash{'shape'},
        };


    return bless $self, $class;
}

sub print_shape {
    
   my $self = shift;
   print $self->{'shape'}->{'line1'} . "\n";
   print $self->{'shape'}->{'line2'} . "\n";
   print $self->{'shape'}->{'line3'} . "\n";
}

1;
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Then use it like this :

use shapes;

my $box;
$box->{line1} =  ' ---';
$box->{line2} =  '|    |';
$box->{line3} =  ' ---';

my $box = shapes->new(shape => $box);
$box->print_shape;
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