#!/usr/bin/perl -w
use strict;
use LWP::Simple qw(get);
use HTML::Parser;
use URI::Escape;

my $new_link = "http://www.baz.com/cgi-bin/doubleclick.cgi?url=";

my $url = $ARGV[0]
    or die "usage: $0 http://www.foo.com/bar.html\n";

my $file     = get($url)
	or die "Cannot get the page '$url'\n";

my $parser = HTML::Parser->new(
    default_h => [ sub { print shift }, 'text' ],
    start_h   => [ \&modify_link, 'tagname, attr, text' ],
)->parse($file);

sub modify_link {
    my ( $tagname, $attr, $text ) = @_;
    print $text and return if $tagname ne 'a';
    $attr->{href} = $new_link . uri_escape( $attr->{href} );
    print '<a', ( map { qq' $_="$attr->{$_}"' } keys %$attr ), '>';
}

__END__