test.pl

package Father;

$VERSION = "0.01";

sub new {
   my $self = {};
   bless $self;
   return $self;
};

sub _internal {
   print "calling Father::_internal\n";
};

sub public {
   shift->_internal();
};

1;

# ====================================

package Child;

use base Father;

$VERSION = "0.01";

sub new {
    my $self = bless {}, shift;
    $self->SUPER::new(@_);
    return $self;
}

sub _internal {
   print "calling Child::_internal\n";
};

# =============================

$a = new Child;
$a->_internal();