您能否提供一些示例说明为什么使用正则表达式难以解析 XML 和 HTML? [英] Can you provide some examples of why it is hard to parse XML and HTML with a regex?
问题描述
我看到人们犯了一个错误 over 和 再次 正在尝试使用正则表达式解析 XML 或 HTML.以下是解析 XML 和 HTML 困难的几个原因:
One mistake I see people making over and over again is trying to parse XML or HTML with a regex. Here are a few of the reasons parsing XML and HTML is hard:
人们希望将文件视为一系列行，但这是有效的:
People want to treat a file as a sequence of lines, but this is valid:
<tag
attr="5"
/>
人们想要对待 <或 <tag 作为标签的开始，但是这样的东西在野外存在:
People want to treat < or <tag as the start of a tag, but stuff like this exists in the wild:
<img src="imgtag.gif" alt="<img>" />
人们通常希望将开始标签与结束标签匹配，但 XML 和 HTML 允许标签包含自己(传统的正则表达式根本无法处理):
People often want to match starting tags to ending tags, but XML and HTML allow tags to contain themselves (which traditional regexes cannot handle at all):
<span id="outer"><span id="inner">foo</span></span>
人们经常希望匹配文档的内容(例如著名的查找给定页面上的所有电话号码"问题)，但数据可能会被标记(即使在查看时看起来很正常):
People often want to match against the content of a document (such as the famous "find all phone numbers on a given page" problem), but the data may be marked up (even if it appears to be normal when viewed):
<span class="phonenum">(<span class="area code">703</span>)
<span class="prefix">348</span>-<span class="linenum">3020</span></span>
评论可能包含格式错误或不完整的标签:
Comments may contain poorly formatted or incomplete tags:
<a href="foo">foo</a>
<!-- FIXME:
<a href="
-->
<a href="bar">bar</a>
您还知道哪些其他问题?
What other gotchas are you aware of?
推荐答案
这里有一些有趣的有效 XML:
Here's some fun valid XML for you:
<!DOCTYPE x [ <!ENTITY y "a]>b"> ]>
<x>
<a b="&y;>" />
<![CDATA[[a>b <a>b <a]]>
<?x <a> <!-- <b> ?> c --> d
</x>
这个小小的快乐是有效的HTML:
And this little bundle of joy is valid HTML:
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd" [
<!ENTITY % e "href='hello'">
<!ENTITY e "<a %e;>">
]>
<title>x</TITLE>
</head>
<p id = a:b center>
<span / hello </span>
&<br left>
<!---- >t<!---> < -->
&e link </a>
</body>
更不用说所有针对无效结构的特定于浏览器的解析.
Not to mention all the browser-specific parsing for invalid constructs.
祝你好运！
编辑(Jörg W Mittag):这是另一个很好的格式良好、有效的 HTML 4.01:
EDIT (Jörg W Mittag): Here is another nice piece of well-formed, valid HTML 4.01:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML/
<HEAD/
<TITLE/>/
<P/>
这篇关于您能否提供一些示例说明为什么使用正则表达式难以解析 XML 和 HTML?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
