use Digest::MD5 qw/md5_hex/;
sub web_MD5 {
    # get MD5 sum of an url
    my $url = shift;
    my $ua = LWP::UserAgent->new(env_proxy => 1,
                 keep_alive => 1,
                 timeout => 30);
    my $response = $ua->get($url);
    unless ($response->is_success) {
      # failed to fetch
      print "Error fetching ", $url, " ",    
      $response->status_line;
    }
    warn "Error while getting ", $response->request->uri,
      " -- ", $response->status_line, "\nAborting";
    unless $response->is_success;
    my $doc = $response->content();
    my $md5 = md5_hex($doc);
    undef $ua;
    return $md5;
}