]*href=(\"??)([^\" >]*?)\\1[^>]*>"; if ( preg_match_all( "/$regexp/siU", $content, $matches, PREG_SET_ORDER ) ) { // $matches might contain parts of $content that has links (a href) preg_match_all( "/$regexp/siU", $content, $matches, PREG_SET_ORDER ); if ( is_array( $matches ) ) { $i = 0; foreach ( $matches as $match ) { $original_tag = $match[0]; // e.g. $tag = $match[0]; // Same value as $original_tag but for further processing $url = $match[2]; // e.g. http://www.example.com/sit-quaerat if ( false !== strpos( $url, get_site_url() ) ) { // Internal link. Do nothing. } elseif ( false === strpos( $url, 'http' ) ) { // Relative link to internal URL. Do nothing. } else { // External link. Let's do something. // Regex pattern for target="_blank|parent|self|top" $pattern = '/target\s*=\s*"\s*_(blank|parent|self|top)\s*"/'; // If there's no 'target="_blank|parent|self|top"' in $tag, add target="blank" if ( 0 === preg_match( $pattern, $tag ) ) { // Replace closing > with ' target="_blank">' $tag = substr_replace( $tag, ' target="_blank">', -1 ); } // If there's no 'rel' attribute in $tag, add rel="noopener noreferrer nofollow" $pattern = '/rel\s*=\s*\"[a-zA-Z0-9_\s]*\"/'; if ( 0 === preg_match( $pattern, $tag ) ) { // Replace closing > with ' rel="noopener noreferrer nofollow">' $tag = substr_replace( $tag, ' rel="noopener noreferrer nofollow">', -1 ); } else { // replace rel="noopener" with rel="noopener noreferrer nofollow" if ( false !== strpos( $tag, 'noopener' ) && false === strpos( $tag, 'noreferrer' ) && false === strpos( $tag, 'nofollow' ) ) { $tag = str_replace( 'noopener', 'noopener noreferrer nofollow', $tag ); } } // Replace original a href tag with one containing target and rel attributes above $content = str_replace( $original_tag, $tag, $content ); } $i++; } } } } return $content; } }