使用perl的Web爬虫

我想开发一个从种子URL开始的Web爬虫,然后抓取它找到的100个html页面,它们与种子URL属于同一个域,并保留遍历的URL的记录,避免重复.我写了以下内容,但$url_count值似乎没有增加,检索到的URL甚至包含来自其他域的链接.我该如何解决这个问题？这里我插入了stackoverflow.com作为我的起始URL.

use strict;
use warnings;

use LWP::Simple;
use LWP::UserAgent;
use HTTP::Request;
use HTTP::Response;


##open file to store links
open my $file1,">>",("extracted_links.txt");
select($file1); 

##starting URL
my @urls = 'https://stackoverflow.com/';

my $browser = LWP::UserAgent->new('IE 6');
$browser->timeout(10);
my %visited;
my $url_count = 0;


while (@urls) 
{
     my $url = shift @urls;
     if (exists $visited{$url}) ##check if URL already exists
     {
         next;
     }
     else
     {
         $url_count++;
     }         

     my $request = HTTP::Request->new(GET => $url);
     my $response = $browser->request($request);

     if ($response->is_error()) 
     {
         printf "%sn",$response->status_line;
     }
     else
     {
         my $contents = $response->content();
         $visited{$url} = 1;
         @lines = split(/n/,$contents);
         foreach $line(@lines)
         {
             $line =~ m@(((http://)|(www.))([a-z]|[A-Z]|[0-9]|[/.]|[~]|[-_]|[()])*[^'">])@g;
             print "$1n";  
             push @urls,$$line[2];
         }

         sleep 60;

         if ($visited{$url} == 100)
         {
            last;
         }
    }
}

close $file1;

#!/usr/bin/env perl

use strict;
use warnings;

use Mojo::UserAgent;
use Mojo::URL;

##open file to store links
open my $log,'>','extracted_links.txt' or die $!;

##starting URL
my $base = Mojo::URL->new('https://stackoverflow.com/');
my @urls = $base;

my $ua = Mojo::UserAgent->new;
my %visited;
my $url_count = 0;

while (@urls) {
  my $url = shift @urls;
  next if exists $visited{$url};

  print "$urln";
  print $log "$urln";

  $visited{$url} = 1;
  $url_count++;         

  # find all <a> tags and act on each
  $ua->get($url)->res->dom('a')->each(sub{
    my $url = Mojo::URL->new($_->{href});
    if ( $url->is_abs ) {
      return unless $url->host eq $base->host;
    }
    push @urls,$url;
  });

  last if $url_count == 100;

  sleep 1;
}