<?php
function bb($stringa)
  {
  $stringa = nl2br($stringa);
  
  $stringa = str_replace("[b]", "<b>", $stringa);
  $stringa = str_replace("[/b]", "</b>", $stringa);
  $stringa = str_replace("[u]", "<u>", $stringa);
  $stringa = str_replace("[/u]", "</u>", $stringa);
  $stringa = str_replace("[i]", "<i>", $stringa);
  $stringa = str_replace("[/i]", "</i>", $stringa);
  
  $stringa = str_replace("[center]", "<center>", $stringa);
  $stringa = str_replace("[/center]", "</center>", $stringa);
  
  $stringa = str_replace("[left]", "<left>", $stringa);
  $stringa = str_replace("[/left]", "</left>", $stringa);
  
  $stringa = str_replace("[right]", "<right>", $stringa);
  $stringa = str_replace("[/right]", "</right>", $stringa);
  $stringa = str_replace(" ", "&nbsp;&nbsp;", $stringa);
    
  $stringa = str_replace(':)','<img src="http://www.sito.it/sr.gif""/>',$stringa);
  $stringa = str_replace(';)','<img src="http://www.sito.it/oc.gif""/>',$stringa);
  $stringa = str_replace(':P','<img src="http://www.sito.it/lg.gif""/>',$stringa);
  $stringa = str_replace(':D','<img src="http://www.sito.it/rs.gif""/>',$stringa);
  //$stringa = str_replace(
  //'...','<img src="http://www.sito.com/img/....gif""/>',$stringa);
  
  $pt = array();
  $sob = array();
  $pt[] = 
  "#\[img\](.*?)\[/img\]#si";
  $sob[] = "<img src=\"\\1\" border=\"0\" />";
  $pt[] = 
  "#\[url\]((www|ftp)\.([\w\-]+\.)*[\w]+(:[0-9]+)?(/[^ \"\n\r\t<]*?)?)\[/url\]#si";
  $sob[] = "<a href=\"http://\\1\">\\1</a>";
  $pt[] = 
  "#\[email\]([a-z0-9\-_.]+?@[\w\-]+\.([\w\-\.]+\.)?[\w]+)\[/email\]#si";
  $sob[] = "<a href=\"mailto:\\1\">\\1</A>";
  
  return @preg_replace($pt, $sob, $stringa);
  }

echo bb(
"[i]ciao[/i] <br> 
  [email]mail@sito.it[/email] <br>
  [url]www.sito.it[/url]
" 
  );
?>