Perl Treebuilder HTML 解析，似乎无法解析到 DIV，出现错误“在模式匹配中使用未初始化的值”

Question

我是使用 Perl 树构建器模块进行 HTML 解析的新手，无法弄清楚这个问题是什么。我花了几个小时试图让它工作并查看了一些教程，但我仍然得到这个错误：“在模式匹配中使用未初始化的值”，指的是我的代码中的这一行：

sub{ $_[0]-> tag() eq 'div' and ($_[0]->attr('class') =~ /snap_preview/)}
        );

此错误在终端中多次打印，我已经一遍又一遍地检查了所有内容，并且它肯定会获取输入，因为 $downloaded 页面是包含我在下面给出的字符串的完整 HTML 文件...非常感谢任何建议。

示例字符串，包含在我的代码的 $downloadedpage 变量中

        <div class='snap_preview'><p><a href="http://recipe4all.com/dishes/mexican/"><img src="http://www.dishbase.com/recipe_images/large/chicken-enchiladas-12005010871.jpg" width="160" height="115" align="left" border="0" alt="Mexican dishes recipes" style="border:none;"></a><a href="http://recipe4all.com/dishes/mexican/"><b>Mexican dishes recipes</b></a> <i></i><br />
Mexican cuisine is popular the world over for its intense flavor and colorful presentation. Traditional Mexican recipes such as tacos, quesadillas, enchiladas and barbacoa are consistently explored for options by some of the world&#8217;s foremost gourmet chefs. A celebration of spices and unique culinary trends, Mexican food is now dominating world cuisines.</p>
<div style="margin-top: 1em" class="possibly-related"><hr /><p><strong>Possibly related posts: (automatically generated)</strong></p><ul><li><a rel='related' href='http://vireja59.wordpress.com/2010/02/13/all-best-italian-dishes-recipes/' style='font-weight:bold'>All best Italian dishes recipes</a></li><li><a rel='related' href='http://vireja59.wordpress.com/2010/05/24/liver-dishes-recipes/' style='font-weight:bold'>Liver dishes recipes</a></li><li><a rel='related' href='http://vireja59.wordpress.com/2010/04/24/parsley-in-cooking/' style='font-weight:bold'>Parsley in cooking</a></li></ul></div>

：

    my $tree = HTML::TreeBuilder->new();
    $tree->parse($downloadedpage);
    $tree->eof();

    #the article is in the div with class "snap_preview"
    @article = $tree->look_down(
    sub{ $_[0]-> tag() eq 'div' and ($_[0]->attr('class') =~ /snap_preview/)}
    );

Answer 1

使用您提供的确切代码和示例，

use warnings;
use strict;
use HTML::TreeBuilder;
my $downloadedpage=<<EOF;
<div class='snap_preview'><p><a href="http://recipe4all.com/dishes/mexican/"><img src="http://www.dishbase.com/recipe_images/large/chicken-enchiladas-12005010871.jpg" width="160" height="115" align="left" border="0" alt="Mexican dishes recipes" style="border:none;"></a><a href="http://recipe4all.com/dishes/mexican/"><b>Mexican dishes recipes</b></a> <i></i><br />
Mexican cuisine is popular the world over for its intense flavor and colorful presentation. Traditional Mexican recipes such as tacos, quesadillas, enchiladas and barbacoa are consistently explored for options by some of the world’s foremost gourmet chefs. A celebration of spices and unique culinary trends, Mexican food is now dominating world cuisines.</p>
<div style="margin-top: 1em" class="possibly-related"><hr /><p><strong>Possibly related posts: (automatically generated)</strong></p><ul><li><a rel='related' href='http://vireja59.wordpress.com/2010/02/13/all-best-italian-dishes-recipes/' style='font-weight:bold'>All best Italian dishes recipes</a></li><li><a rel='related' href='http://vireja59.wordpress.com/2010/05/24/liver-dishes-recipes/' style='font-weight:bold'>Liver dishes recipes</a></li><li><a rel='related' href='http://vireja59.wordpress.com/2010/04/24/parsley-in-cooking/' style='font-weight:bold'>Parsley in cooking</a></li></ul></div>
EOF

my $tree = HTML::TreeBuilder->new();
    $tree->parse($downloadedpage);
    $tree->eof();

    #the article is in the div with class "snap_preview"
    my @article = $tree->look_down(
    sub{ $_[0]-> tag() eq 'div' and ($_[0]->attr('class') =~ /snap_preview/)}
    );

我根本没有收到任何错误。我的第一个猜测是 HTML 中有一些没有 class 属性的

。

也许你需要

sub{
     $_[0]-> tag() eq 'div' and 
     $_[0]->attr('class') and 
     ($_[0]->attr('class') =~ /snap_preview/)
}

在那里写？