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How can one parse and process HTML/XML in PHP?

How can one parse HTML/XML and extract information from it?

phpQuery and QueryPath are extremely similar in replicating the fluent jQuery API. That's also why they're two of the easiest approaches to properly parse HTML in PHP.

Examples for QueryPath

Basically you first create a queryable DOM tree from an HTML string:

 $qp = qp("<html><body>

title

..."); // or give filename or URL

The resulting object contains a complete tree representation of the HTML document. It can be traversed using DOM methods. But the common approach is to use CSS selectors like in jQuery:

 $qp->find("div.classname")->children()->...;

 foreach ($qp->find("p img") as $img) {
     print qp($img)->attr("src");
 }

Mostly you want to use simple #id and .class or DIV tag selectors for ->find(). But you can also use XPath statements, which sometimes are faster. Also typical jQuery methods like ->children() and ->text() and particularly ->attr() simplify extracting the right HTML snippets. (And already have their SGML entities decoded.)

 $qp->xpath("//div/p[1]");  // get first paragraph in a div

QueryPath also allows injecting new tags into the stream (->append), and later output and prettify an updated document (->writeHTML). It can not only parse malformed HTML, but also various XML dialects (with namespaces), and even extract data from HTML microformats (XFN, vCard).

 $qp->find("a[target=_blank]")->toggleClass("usability-blunder");

.

phpQuery or QueryPath?

Generally QueryPath is better suited for manipulation of documents. While phpQuery also implements some pseudo AJAX methods (just HTTP requests) to more closely resemble jQuery. It is said that phpQuery is often faster than QueryPath (because of fewer overall features).

For further information on the differences see this comparison on the wayback machine from tagbyte.org. (Original source went missing, so here's an internet archive link. Yes, you can still locate missing pages, people.)

And here's a comprehensive QueryPath introduction.

Advantages

  • Simplicity and Reliability
  • Simple to use alternatives ->find("a img, a object, div a")
  • Proper data unescaping (in comparison to regular expression grepping)
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Why you shouldn't and when you should use regular expressions?

First off, a common misnomer: Regexps are not for "parsing" HTML. Regexes can however "extract"data. Extracting is what they're made for. The major drawback of regex HTML extraction over proper SGML toolkits or baseline XML parsers are their syntactic effort and varying reliability.

Consider that making a somewhat dependable HTML extraction regex:

]+id="(d+)".+?    ]+href="(http://[^">]+)"[^>]*>([^<>]+).+?

is way less readable than a simple phpQuery or QueryPath equivalent:

$div->find(".stationcool a")->attr("title");

There are however specific use cases where they can help.

  • Many DOM traversal frontends don't reveal HTML comments <!--, which however are sometimes the more useful anchors for extraction. In particular pseudo-HTML variations <$var>or SGML residues are easy to tame with regexps.
  • Oftentimes regular expressions can save post-processing. However HTML entities often require manual caretaking.
  • And lastly, for extremely simple tasks like extracting </> <>>/&> > <><>>  href="http://fossil.include-once.org/streamtuner2/" rel="noreferrer">app, where I employ XML parsing and regular expressions alternatively. Just last week the PyQuery parsing broke, and the regex still worked. Yes weird, and I can't explain it myself. But so it happened.
    So please don't vote real-world considerations down, just because it doesn't match the regex=evil meme. But let's also not vote this up too much. It's just a sidenote for this topic.

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Try Simple HTML DOM Parser

  • A HTML DOM parser written in PHP 5+ that lets you manipulate HTML in a very easy way!
  • Require PHP 5+.
  • Supports invalid HTML.
  • Find tags on an HTML page with selectors just like jQuery.
  • Extract contents from HTML in a single line.
  • Download

 

Examples:

 

How to get HTML elements:

// Create DOM from URL or file
$html = file_get_html('http://www.example.com/');

// Find all images
foreach($html->find('img') as $element)
       echo $element->src . '
'; // Find all links foreach($html->find('a') as $element) echo $element->href . '
';

 

How to modify HTML elements:

// Create DOM from string
$html = str_get_html('
Hello
World
'); $html->find('div', 1)->class = 'bar'; $html->find('div[id=hello]', 0)->innertext = 'foo'; echo $html;

 

Extract content from HTML:

// Dump contents (without tags) from HTML
echo file_get_html('http://www.google.com/')->plaintext;

 

Scraping Slashdot:

// Create DOM from URL
$html = file_get_html('http://slashdot.org/');

// Find all article blocks
foreach($html->find('div.article') as $article) {
    $item['title']     = $article->find('div.title', 0)->plaintext;
    $item['intro']    = $article->find('div.intro', 0)->plaintext;
    $item['details'] = $article->find('div.details', 0)->plaintext;
    $articles[] = $item;
}

print_r($articles);
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Native XML Extensions

I prefer using one of the native XML extensions since they come bundled with PHP, are usually faster than all the 3rd party libs and give me all the control I need over the markup.

DOM

The DOM extension allows you to operate on XML documents through the DOM API with PHP 5. It is an implementation of the W3C's Document Object Model Core Level 3, a platform- and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure and style of documents.

DOM is capable of parsing and modifying real world (broken) HTML and it can do XPath queries. It is based on libxml.

It takes some time to get productive with DOM, but that time is well worth it IMO. Since DOM is a language-agnostic interface, you'll find implementations in many languages, so if you need to change your programming language, chances are you will already know how to use that language's DOM API then.

A basic usage example can be found in Grabbing the href attribute of an A element and a general conceptual overview can be found at DOMDocument in php

How to use the DOM extension has been covered extensively on StackOverflow, so if you choose to use it, you can be sure most of the issues you run into can be solved by searching/browsing Stack Overflow.

XMLReader

The XMLReader extension is an XML pull parser. The reader acts as a cursor going forward on the document stream and stopping at each node on the way.

XMLReader, like DOM, is based on libxml. I am not aware of how to trigger the HTML Parser Module, so chances are using XMLReader for parsing broken HTML might be less robust than using DOM where you can explicitly tell it to use libxml's HTML Parser Module.

A basic usage example can be found at getting all values from h1 tags using php

XML Parser

This extension lets you create XML parsers and then define handlers for different XML events. Each XML parser also has a few parameters you can adjust.

The XML Parser library is also based on libxml, and implements a SAX style XML push parser. It may be a better choice for memory management than DOM or SimpleXML, but will be more difficult to work with than the pull parser implemented by XMLReader.

SimpleXml

The SimpleXML extension provides a very simple and easily usable toolset to convert XML to an object that can be processed with normal property selectors and array iterators.

SimpleXML is an option when you know the HTML is valid XHTML. If you need to parse broken HTML, don't even consider SimpleXml because it will choke.

A basic usage example can be found at A simple program to CRUD node and node values of xml file and there is lots of additional examples in the PHP Manual.


3rd Party Libraries (libxml based)

If you prefer to use a 3rd-party lib, I'd suggest using a lib that actually uses DOM/libxml underneath instead of string parsing.

FluentDom - Repo

FluentDOM provides a jQuery-like fluent XML interface for the DOMDocument in PHP. Selectors are written in XPath or CSS (using a CSS to XPath converter). Current versions extend the DOM implementing standard interfaces and add features from the DOM Living Standard. FluentDOM can load formats like JSON, CSV, JsonML, RabbitFish and others. Can be installed via Composer.

HtmlPageDom

Wa72HtmlPageDom` is a PHP library for easy manipulation of HTML documents using It requires DomCrawler from Symfony2 components for traversing the DOM tree and extends it by adding methods for manipulating the DOM tree of HTML documents.

phpQuery (not updated for years)

phpQuery is a server-side, chainable, CSS3 selector driven Document Object Model (DOM) API based on jQuery JavaScript Library written in PHP5 and provides additional Command Line Interface (CLI).

Also see: https://github.com/electrolinux/phpquery

Zend_Dom

Zend_Dom provides tools for working with DOM documents and structures. Currently, we offer Zend_Dom_Query, which provides a unified interface for querying DOM documents utilizing both XPath and CSS selectors.

QueryPath

QueryPath is a PHP library for manipulating XML and HTML. It is designed to work not only with local files, but also with web services and database resources. It implements much of the jQuery interface (including CSS-style selectors), but it is heavily tuned for server-side use. Can be installed via Composer.

fDOMDocument

fDOMDocument extends the standard DOM to use exceptions at all occasions of errors instead of PHP warnings or notices. They also add various custom methods and shortcuts for convenience and to simplify the usage of DOM.

sabre/xml

sabre/xml is a library that wraps and extends the XMLReader and XMLWriter classes to create a simple "xml to object/array" mapping system and design pattern. Writing and reading XML is single-pass and can therefore be fast and require low memory on large xml files.

FluidXML

FluidXML is a PHP library for manipulating XML with a concise and fluent API. It leverages XPath and the fluent programming pattern to be fun and effective.


3rd-Party (not libxml-based)

The benefit of building upon DOM/libxml is that you get good performance out of the box because you are based on a native extension. However, not all 3rd-party libs go down this route. Some of them listed below

PHP Simple HTML DOM Parser

  • An HTML DOM parser written in PHP5+ lets you manipulate HTML in a very easy way!
  • Require PHP 5+.
  • Supports invalid HTML.
  • Find tags on an HTML page with selectors just like jQuery.
  • Extract contents from HTML in a single line.

I generally do not recommend this parser. The codebase is horrible and the parser itself is rather slow and memory hungry. Not all jQuery Selectors (such as child selectors) are possible. Any of the libxml based libraries should outperform this easily.

PHP Html Parser

PHPHtmlParser is a simple, flexible, html parser which allows you to select tags using any css selector, like jQuery. The goal is to assiste in the development of tools which require a quick, easy way to scrap html, whether it's valid or not! This project was original supported by sunra/php-simple-html-dom-parser but the support seems to have stopped so this project is my adaptation of his previous work.

Again, I would not recommend this parser. It is rather slow with high CPU usage. There is also no function to clear memory of created DOM objects. These problems scale particularly with nested loops. The documentation itself is inaccurate and misspelled, with no responses to fixes since 14 Apr 16.

Ganon

  • A universal tokenizer and HTML/XML/RSS DOM Parser
    • Ability to manipulate elements and their attributes
    • Supports invalid HTML and UTF8
  • Can perform advanced CSS3-like queries on elements (like jQuery -- namespaces supported)
  • A HTML beautifier (like HTML Tidy)
    • Minify CSS and Javascript
    • Sort attributes, change character case, correct indentation, etc.
  • Extensible
    • Parsing documents using callbacks based on current character/token
    • Operations separated in smaller functions for easy overriding
  • Fast and Easy

Never used it. Can't tell if it's any good.


HTML 5

You can use the above for parsing HTML5, but there can be quirks due to the markup HTML5 allows. So for HTML5 you want to consider using a dedicated parser, like

html5lib

A Python and PHP implementations of a HTML parser based on the WHATWG HTML5 specification for maximum compatibility with major desktop web browsers.

We might see more dedicated parsers once HTML5 is finalized. There is also a blogpost by the W3's titled How-To for html 5 parsing that is worth checking out.


WebServices

If you don't feel like programming PHP, you can also use Web services. In general, I found very little utility for these, but that's just me and my use cases.

ScraperWiki.

ScraperWiki's external interface allows you to extract data in the form you want for use on the web or in your own applications. You can also extract information about the state of any scraper.


Regular Expressions

Last and least recommended, you can extract data from HTML with regular expressions. In general using Regular Expressions on HTML is discouraged.

Most of the snippets you will find on the web to match markup are brittle. In most cases they are only working for a very particular piece of HTML. Tiny markup changes, like adding whitespace somewhere, or adding, or changing attributes in a tag, can make the RegEx fails when it's not properly written. You should know what you are doing before using RegEx on HTML.

HTML parsers already know the syntactical rules of HTML. Regular expressions have to be taught for each new RegEx you write. RegEx are fine in some cases, but it really depends on your use-case.

You can write more reliable parsers, but writing a complete and reliable custom parser with regular expressions is a waste of time when the aforementioned libraries already exist and do a much better job on this.

Also see Parsing Html The Cthulhu Way


Books

If you want to spend some money, have a look at

I am not affiliated with PHP Architect or the authors.

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