fun-custom.php

<?php
/**
 * 其他外部引用函数方法
 * ==================
 */

/**
 * 给外链加上nofollow及新窗口打开
 * from: https://cn.wordpress.org/plugins/nofollow-for-external-link/
 * license: GPL-2.0
 */
if(!function_exists('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;
    }
}
add_filter( 'the_content', 'cn_nf_url_parse');