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Create Your Own BBCode
By dave

Online forums (message boards, bulletin boards, or whatever you wanna call them) often support BBCode. Not sure what I'm talking about? Here's an example:
[url=http://www.nutang.com]NuTang Weblog Community[/url]
Should be converted to..
<a href="http://www.nutang.com">NuTang Weblog Community</a>

In this tutorial, I'll teach how, using PHP, you can parse a block of text and convert the BBCode into HTML. The function in the spotlight here is preg_replace. To fully understand its use, you should be familiar with regular expressions. If you aren't, just skim my regular expressions tutorial [http://www.icemelon.com/tutorials/1/Regular_Expressions.htm].

First, let's lay down a few assumptions. I'll assume the text you wanna parse is stored in the variable $stuff. Now, let's just get down to the code:
// convert [url=URL]link_title[/url]
$pattern[] = '/\[url=(.*?)\](.*?)\[\/url\]/i';
$replace[] = '<a href="$1">$2</a>';

// convert [url]url_link[/url]
$pattern[] = '/\[url\](.*?)\[\/url\]/i';
$replace[] = '<a href="$1">$1</a>';

// convert [img]image_link[/img]
$pattern[] = '/\[img\](.*?)\[\/img\]/i';
$replace[] = '<img src="$1">';

// convert [b]text[/b]
$pattern[] = '/\[b\](.*?)\[\/b\]/i';
$replace[] = '<b>$1</b>';

// convert [code]CODE[/code]
$pattern[] = '/\[code\](.*?)\[\/code\]/i';
$replace[] = '<xmp>$1</xmp>';

$html = preg_replace($pattern, $replace, $stuff);

The above code supports the following BBCode tags: [url], [img], [code], & [b]. Let's just go over one example, because as you can see, they're all variations of the same structure. Let's look at [b], which converts text to be boldfaced:
// convert [b]text[/b]
preg_match('/\[b\](.*?)\[\/b\]/i', '<b>$1</b>', $stuff);
Remember, stuff that fits the expression within the parentheses will be stored in $1 (then $2, $3, etc., if applicable). In the above example, we only have one set of parentheses, so we only need to worry about $1. The $1 will store the text to be boldfaced. Further note, a lot of characters need to be escaped (using '\'). (Again, check out details about the function here: preg_replace).

  • What's with the "(.*?)" ? Why not just use "(.*)" ? I actually don't quite understand that myself, but if you try the second version, things will not work out the way you want. You will lose A LOT of matches.
  • Can't I just use str_replace? Good observation. You certainly can, and it would be more efficient. However, preg_match was used in the examples, because it is more powerful. You can manipulate your "$stuff" a lot more, especially with this function: preg_replace_callback.

    Speaking of str_replace, you should use this function to convert your smilies. For instance:
    // converts ;-) to a wink-smilie
    $html = str_replace(';-)', '<img src=images/smilies/wink.gif>', $html);

    More Related Functions
  • preg_match
  • preg_match_all
  • substr_replace
  • str_ireplace
  • ereg_replace
  • preg_split

    Okay, I think I've run out of things to say. It's a wrap!
  • P.S. Check out my new site TheManWhoSoldtheWeb.com, where I publish guides and scripts on Internet Marketing and SEO. Here is a limited time freebie: the Rapid Google Indexer.

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