1 #!/usr/local/bin/perl
  2 use strict;
  3 use warnings;
  4 use LWP::Simple;
  5 use HTML::TreeBuilder::XPath;
  6 use Data::Dumper;
  7 use feature 'say';
  8 my $url="http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/pdbsum/GetPage.pl?pdbcode=1r9t&template=main.html";
  9
 10 my $p = HTML::TreeBuilder::XPath->new_from_content(get($url));
 11
 12 my @chain_tags = $p->findnodes("//td//a[contains(\@href,'chain=')]");
 13 my $uniq_chains = { map { $_->attr('href') =~ /chain=(\w)/; ($1,1); } @chain_tags };
 14 say " Number of chains : " . scalar keys %$uniq_chains;
 15 say keys %$uniq_chains;