PHP regular expression in action: matching XML documents

<p>With the development of the Internet, XML documents are becoming more and more common, so we need to understand how to use regular expressions to match content in XML documents. This article will introduce you to the practical application of PHP regular expressions to help developers better process and analyze XML documents. </p> <p>What is an XML document? </p> <p>XML (Extensible Markup Language) is a markup language used to store and transmit data. XML documents consist of tags, attributes and content. Tags are descriptions used to identify data, attributes are some special information in tags, and content is the data described by tags. </p> <p>For example: </p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:xml;toolbar:false;'><book genre="mystery"> <title>The Hound of the Baskervilles</title> <author>Arthur Conan Doyle</author> <price>5.99</price> </book></pre><div class="contentsignin">Copy after login</div></div><p>Here <code>book</code> is the tag, <code>genre</code> is the attribute, <code>The Hound of the Baskervilles</code> is the content . XML documents can contain any number of tags, attributes and content. </p><p>How to match XML documents using PHP regular expressions? </p><p>In PHP, you can use the <code>preg_match()</code> function to match XML documents. This function takes three parameters: the regular expression, the string to match, and an optional array to store the match results. </p><p>The following is an example that demonstrates how to use regular expressions to match tags in XML documents: </p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>$xml = '<book genre="mystery"> <title>The Hound of the Baskervilles</title> <author>Arthur Conan Doyle</author> <price>5.99</price> </book>'; $pattern = '/<([a-zA-Z0-9]+)>/'; preg_match($pattern, $xml, $matches); print_r($matches);</pre><div class="contentsignin">Copy after login</div></div><p>The output is as follows: </p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>Array ( [0] => <book> [1] => book )</pre><div class="contentsignin">Copy after login</div></div><p>The regular expression here The formula <code>/<([a-zA-Z0-9] )>/</code> can match tags in XML documents. <code>([a-zA-Z0-9] )</code> means matching one or more uppercase and lowercase letters and numeric characters. <code><</code> and <code>></code> represent the beginning and end of tags. </p><p>During the matching process, the <code>preg_match()</code> function will search for substrings that match the regular expression in the string and store the matching results in the <code>$matches</code> array middle. <code>$matches[0]</code> represents the entire substring that matches the regular expression, <code>$matches[1]</code> represents the substring within the first bracket in the regular expression. </p><p>The following are some other commonly used regular expressions: </p><p> Matching attributes: </p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>$pattern = '/([a-zA-Z]+)="([^"]+)"/'; preg_match($pattern, $xml, $matches); print_r($matches);</pre><div class="contentsignin">Copy after login</div></div><p>The output results are as follows: </p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>Array ( [0] => genre="mystery" [1] => genre [2] => mystery )</pre><div class="contentsignin">Copy after login</div></div><p>Regular expression here<code>/([a-zA-Z] )="([^"] )"/</code> can match attributes in XML documents. <code>([a-zA-Z] )</code> means matching one or multiple uppercase and lowercase letters, <code>="</code> indicates the beginning of the attribute, <code>([^"] )</code> indicates matching any character except double quotes, <code>"</code> Indicates the end of the attribute. </p><p> Matching content: </p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>$pattern = '/<title>([^<]+)</title>/'; preg_match($pattern, $xml, $matches); print_r($matches);</pre><div class="contentsignin">Copy after login</div></div><p>The output result is as follows: </p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>Array ( [0] => <title>The Hound of the Baskervilles</title> [1] => The Hound of the Baskervilles )</pre><div class="contentsignin">Copy after login</div></div><p>The regular expression here<code>/<title>([^<] )</ title>/</code> can match the content of the <code><title></code> tag in the XML document. <code>([^<] )</code> means matching any character except the less than sign, <code></title></code> means matching the <code></title></code> tag Finish. </p> <p>Summary</p> <p> PHP regular expressions are a very useful tool when processing XML documents. By using regular expressions, we can easily match, extract and process data in XML documents. However, it should be noted that regular expressions are not very efficient. When dealing with large XML documents, it is recommended to use a specialized XML parser to process the data. </p>

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