Very simple bbcode

<?php
  function bbcode($data)
  {
          $input = array(
                  '/\[b\](.*?)\[\/b\]/is',
                  '/\[i\](.*?)\[\/i\]/is',
                  '/\[u\](.*?)\[\/u\]/is',
                  '/\[img\](.*?)\[\/img\]/is',
                  '/\[url\](.*?)\[\/url\]/is',
                  '/\[url\=(.*?)\](.*?)\[\/url\]/is'
                  );

          $output = array(
                  '<strong>$1</strong>',
                  '<em>$1</em>',
                  '<u>$1</u>',
                  '<img src="$1" />',
                  '<a href="$1">$1</a>',
                  '<a href="$1">$2</a>'
                  );

          $rtrn = preg_replace ($input, $output, $data);

          return $rtrn;
  }
$bcode = $bbcode('[i]this is testing text[/i]');// This is how you use it on a forum or a page

echo $bcode;//output: <strong>this is again another test text</strong>
?>