W Post Content Link Replacement

dw-post-content-link-replacement.php

<?php
/**
 * Plugin Name: DW Post Content Link Replacement
 * Description: Add target="_blank" and rel="nofollow" to links.
 * Version: 1.0
 * Author: DesignWall
 * Author URI: http://www.designwall.com/
 * License: GPLv3 or later
**/

function dw_link_replace_target($text) {
  $new_text = str_replace('<a', '<a target="_blank"', $text);
  return $new_text;
}
add_filter('the_content', 'dw_link_replace_target');

function dw_link_replace_rel ($text) {
  $new_text = str_replace('<a', '<a rel="nofollow"', $text);
  return $new_text;
}
add_filter('the_content', 'dw_link_replace_rel');
?>