[php] Replacing certain characters within a part of a string.

I wrote this script because on my blog dangerous characters(", &, <, >) get replaced with their html(?) equilavent before inserting an entry/comment in to the database. Normally this isn't a problem but the highlight_string function in php doesn't display the characters normally.

Example:

Code:

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<?php echo "test"; ?>

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Non-highlighted outputs:

Code:

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<?php echo "test"; ?>

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Highlighted with highlight_string outputs:

PHP Code:

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<?php echo "test"; ?> 


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Highlighted with my script:

PHP Code:

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<?php echo "test"; ?>

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How does it work?
The to-be replaced part of the string must be put between [tag][/tag] tags (or any other tag you prefer) The rest of the script is explained in the comments.

Bugs:
If tags are incorrectly nested or left un-closed the script doesn't work properly.

The script:

PHP Code:

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<?php
//Define a string
$str = "[tag]&lt;?php echo &quot;test&quot;; ?&gt;[/tag]";

//Get the parts that need to be replaced.
preg_match_all("/\[tag](.*?)\[\/tag]/is", $str, $matches, PREG_SET_ORDER);

$i = 0;

//Use a while loop to replace all the parts that need to be replaced one by one.
while($i < count($matches)) {
    
    //Replace the html-chars with their equilavent counter-parts.
    $code = highlight_string(preg_replace(array('/\&amp\;/','/\&lt\;/','/\&gt\;/','/\&quot\;/'), array('&', '<', '>', '"'), $matches[$i][1]), true);
    
    //Put above line in the complete string.
    $str = preg_replace("/\[tag](.*?)\[\/tag]/is", $code, $str, 1);
    
    $i ++;

}

echo $str;
?>

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Thought I'd share it, because I found it quite useful. ^^

Ah, you got it to work :), nice ;)