The PHP Execution plugin allows embedding php code inside of posts and pages.

The PHP Execution Plugin is a WordPress plugin which allows users to write php code inside of their posts and pages. Embedded php code will be executed when the post is shown. In doing so, the plugin offers the possibility to utilize dynamic content inside of posts.
In contrast to other plugins with the same aim, this one integrates well with WordPress’ visual editor. So there is no need to turn off the visual editor in order to edit your php code. 
Additionally it provides an admin section which lets administrators edit the blog users’ php execution rights easily. The plugin also automatically prevents users with no php execution rights from editing posts or pages of users with these rights. It thus fixes a possible security leak where people without php execution rights can still execute code with editing other users’ posts.
Features:
<ul>
<li>executes php code in your posts and pages (full, excerpts, feeds).</li>
<li>integrates well with WordPress’ visual editor. No need to turn it off.</li>
<li>write php code in the usual ” syntax in the html view of the editor.</li>
<li>admin section to edit the blog users’ php execution rights.</li>
<li>plugin automatically prevents users with no php execution rights to edit posts of users with rights to execute php code.</li>
</ul>
Project was now moved out of beta.
Further information at <a href="http://www.zehnet.de/2009/02/25/wordpress-php-execution-plugin/" title="PHP Execution home" rel="nofollow ugc">zehnet.de: PHP Execution Plugin home</a>
<h3>Editing PHP code</h3>
<ul>
<li>php code can be edited in the html view of the editor.</li>
<li>php code is embedded into a post in the same way as you are used to: a php block begins with ”. The short open tag, i.e. ”) somewhere inside a string in your php code block. If you do so, this ending delimeter will be matched and your code will inevitably break apart. So don?t write e.g.:</li>
</ul>
<pre>
 some text
 <?php $test = "hello ?>" ?>
 more text
</pre>
<ul>
<li>Writing ‘$test = “hello ?&gt;”‘ instead will not lead to any problems.</li>
<li>Php code is not executed in the global scope. If you need to gain access to variables in the global scope you need to “import” them first with ‘global $var1, $var2;’.</li>
<li>This plugin does not evaluate every single code snippet, but the content of the post as a whole. So the following lines won?t result in errors:</li>
</ul>
<pre>
 <?php if ($test==true) { ?>
 The test was successful.
 <?php } else { ?>
 The test failed.
 <?php } ?>
</pre>
<ul>
<li>When switching between html and visual view the php code is not altered in any case. All html tags, whitespaces etc. in your code are preserved.</li>
</ul>

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