Please put your code in <code> tages. See How do I post a question effectively?

Update:
Run this you should have your result: Modified OP script

use warnings;
use strict;

use LWP::Simple;
use URI::Escape;
use HTML::TreeBuilder;
use Try::Tiny;

my $look_for = "perl";
my $contents =
  get
"http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dstripbooks&
+field-keywords="
  . uri_escape($look_for);
my $html = HTML::TreeBuilder->new_from_content($contents);
for my $item ( $html->look_down( id => qr/result_\d+/ ) ) {

    #$item->dump;
    #find out structure of HTML
    my $author =
      try { $item->look_down( class => 'ptBrand' )->as_trimmed_text };
    print "$author\n";
}
$html->delete;
[download]

by Randal L. Schwartz, brian d foy and Tom Phoenix
by Tom Christiansen, brian d foy, Larry Wall and Jon Orwant Ph.D.
by Tom Christiansen and Nathan Torkington
by Randal L. Schwartz, brian d foy and Tom Phoenix
by Johan Vromans
by Joseph N. Hall, Joshua A. McAdams and brian d foy
by Randal Schwartz, Tom Phoenix and brian d foy
by David N. Blank-Edelman
by brian d foy
by Curtis Poe
by Damian Conway
by Paul E. Hoffman
[download]