Regex a user name and append to a URL in template?

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This is my first post and I'm jumping in head first so please bear with me.

I want to format a user name removing unusable characters, and then append that user name to a URL for IRC chat. I'm not 100% sure I can do this in a template for a widget nor am I 100% sure how to code it. Any help would be appreciated. I know the code below is wrong, but it should be clear what I am trying to accomplish.

Thanks

PHP Code:

<div class="cms_widget"> 
  <div class="block"> 
    <div class="cms_widget_header widget_header"> 
       <h3>IRC Chat</h3> 
    </div> 
  <div class="cms_widget_content widget_content"> 

      Dirty = $bbuserinfo[username]

      $Clean = preg_replace('/^[0-9]+([^0-9])/', '\\1', preg_replace('/[^-a-zA-Z0-9_|^{}[\]\\\\]/', '', $Dirty));}

      $Output = 'http://www.somesite.com/chat&user='$Clean
  

    </div> 
   </div> 
</div>