[b]test[/b]
[url=http://blah.com]blah[/url]

<strong>test</strong>
<a href="http://blah.com" target="_blank">blah</a>

function ubbcode($posting) {
        $posting=eregi_replace("\[img\]([^\[]+)\[/img\]","<img src=\"\\1\" border=\"0\">",$posting);
        $posting=eregi_replace("\[email\]([^\[]+)\[/email\]","<a href=\"mailto:\\1\">\\1</a>",$posting);
        $posting=eregi_replace("\[email=([^\[]+)\]([^\[]+)\[/email\]","<a href=\"mailto:\\1\">\\2</a>",$posting);
        $posting=eregi_replace("\[url=([^\[]+)\]([^\[]+)\[/url\]","<a href=\"\\1\" target=\"_blank\">\\2</a>",$posting);
        $posting=eregi_replace("\[url\]([^\[]+)\[/url\]","<a href=\"\\1\" target=\"_blank\">\\1</a>",$posting);
    $posting=eregi_replace("\[b\]","<strong>",$posting);
    $posting=eregi_replace("\[/b\]","</strong>",$posting);
    $posting=eregi_replace("\[u\]","<u>",$posting);
    $posting=eregi_replace("\[/u\]","</u>",$posting);
    $posting=eregi_replace("\[i\]","<em>",$posting);
    $posting=eregi_replace("\[/i\]","</em>",$posting);

    return $posting;
}