// 文章页面外链自动添加nofollow属性和新窗口打开
add_filter( 'the_content', 'cn_nf_url_parse');
function cn_nf_url_parse( $content ) {
    $regexp = "<a\\s[^>]*href=(\\"??)([^\\" >]*?)\\\\1[^>]*>";
    if(preg_match_all("/$regexp/siU", $content, $matches, PREG_SET_ORDER)) {
        if( !empty($matches) ) {
            $srcUrl = get_option('siteurl');
            for ($i=0; $i < count($matches); $i++) {
                $tag = $matches[$i][0];
                $tag2 = $matches[$i][0];
                $url = $matches[$i][0];
                $noFollow = '';
                $pattern = '/target\\s*=\\s*\"\\s*_blank\\s*\"/';
                preg_match($pattern, $tag2, $match, PREG_OFFSET_CAPTURE);
                if( count($match) < 1 )
                    $noFollow .= ' target=\"_blank\" ';
                $pattern = '/rel\\s*=\\s*\"\\s*[n|d]ofollow\\s*\"/';
                preg_match($pattern, $tag2, $match, PREG_OFFSET_CAPTURE);
                if( count($match) < 1 )
                    $noFollow .= ' rel=\"nofollow\" ';
                $pos = strpos($url,$srcUrl);
                if ($pos === false) {
                    $tag = rtrim ($tag,'>');
                    $tag .= $noFollow.'>';
                    $content = str_replace($tag2,$tag,$content);
                }
            }
        }
    }
    $content = str_replace(']]>', ']]>', $content);
    return $content;
}