注释代码的正则表达式问题

Question

I am currently making a homepage where logged in users can write comments. The comment string is first run through a function that str_replaces emoticons. After that I want it to exchange

[url=www.whatever.com]linktext[/url]

with:

<a href='www.whatever.com'>linktext</a>

The reason for this is that I want to strip the text for all the html code that isn't controlled by my comment code, in case some users decide to get creative-

and thought it would be best to use preg replace but the code I ended up with (Partially from reading about reg exp from my trusty "O reilly Sql and Php"-book and partially from the web) Is pretty bonkers, and most importantly, doesn't work.

Any help would be appreciated, thanks.

It's probably possible to exchange the entire code, not in 2 segments like I have done. Just decided on that getting 2 smaller parts to work first would be easier, and then merge them afterwards.

code:

function text_format($string)
{
    $pattern="/([url=)+[a-zA-Z0-9]+(])+/";
    $string=preg_replace($pattern, "/(<a href=\')+[a-zA-Z0-9]+(\'>)+/", $string);
    $pattern="/([\/url])+/";
    $string=preg_replace($pattern, "/(<\/a>)+/", $string);    
    return $string;
}

Answer 1

I experimented a bit with the following:

function text_format($string)
{
    return preg_replace('#\[url=([^\]]+)\]([^\[]*)\[/url\]#', '<a href="$1">$2</a>', $string);
}

However, one immediate fault with this is that if linktext is empty, there will be nothing between <a> and </a>. One way around it would be to do another pass with something like this:

preg_replace('#<a href="([^"]+)"></a>#', '<a href="$1">$1</a>', $string);

Another option would be to use preg_replace_callback and put this logic inside your callback function.

Finally, this is obviously a common "problem" and has been solved many times by others, and if using a more mature open sourced solution is an option, I'd recommend looking for one.