thanks you solved my question, is it enough if I put there solved and paste your code below???For beginner like me, I suggest to read the previews posts

#!/usr/bin/perl

use warnings;
use strict;
use LWP::Simple;
use HTML::TreeBuilder;

print "ELENCO LIGANDI\n";

my $url3 = "http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum
+/GetPage.pl?pdbcode=2j6p&template=ligands.html&l=1.1";
my $content =get ($url3);

my $p = HTML::TreeBuilder->new;
$p->parse_content($content);

my @anchors = $p->look_down(_tag => q{a});
for my $anchor (@anchors){
  my $txt = $anchor->as_text;  
  if ($txt=~ /EPE\s/){
    print $txt, qq{\n};
    my $href = $anchor->attr(q{href});
    print $href, qq{\n};
  }
}
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