#!/usr/bin/perl

package FilterDiv;
require HTML::Filter;
@ISA = qw(HTML::Filter);

sub start {
    my $self = shift;
    $self->{div_seen}++ if $_[0] eq "div";
    $self->SUPER::start(@_);
}

sub end {
    my $self = shift;
    $self->SUPER::end(@_);
    $self->{div_seen}-- if $_[0] eq "div";
}

sub output {
    my $self = shift;
    unless ( $self->{div_seen} ) {
        $self->SUPER::output(@_);
    }
}
1;

my $p = FilterDiv->new or die;
$p->parse_file(*DATA) or die;

__DATA__
<!-- aaaa --><b>a</b>
<div  
>
123<div >aaaa</div>
Text
<div ..
>a</div                      >
..
</div


>
Text