replacing a custom tag's value with a string in php

I want to read a html file and replace what ever is inside mytag.

so in html file we have something like this :

                    <div>
                        <h3><mytag>_THIS_DAY</mytag></h3>
       开发者_如何学Python                 <div>
                             [LOGIN]
                        </div>
                    </div>

and then in php file , i need to read the file and replace the values inside tags.

str_replace() ?

how to get the value inside those tags in php and then how to replace them with something like a string ?

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str_replace() uses regular expressions, which (as noted elsewhere on this site) are usually insufficient for parsing HTML.

You should use an HTML parser to retrieve and/or replace the required values.

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Warning: You shouldn't parse XHTML with regexp

That said, you can still do it:

preg_replace("~(?<=<mytag>)[^>]+(?=</mytag>)~", "independance day", $yourHtml);

Quick explanation:

• [^>]+ We look for a string of 1+ char and without >
• (?<=<mytag>) This string must be after <mytag> (positive lookahead)
• (?=</mytag>) This string must be folowed by </mytag> (positive lookbehind)

Live example

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• take a look in the php-manual fpr preg_replace. with a regex you can perform a simple replacement
• if you want to something more complex, you can parse your html. you can use for example the simple_html_dom-contribution: http://simplehtmldom.sourceforge.net/