1function rd_duplicate_post_as_draft(){
  2  global $wpdb;
  3  if (! ( isset( $_GET['post']) || isset( $_POST['post'])  || ( isset($_REQUEST['action']) && 'rd_duplicate_post_as_draft' == $_REQUEST['action'] ) ) ) {
  4    wp_die('No post to duplicate has been supplied!');
  5  }
  6 
  7  /*
  8   * Nonce verification
  9   */
 10  if ( !isset( $_GET['duplicate_nonce'] ) || !wp_verify_nonce( $_GET['duplicate_nonce'], basename( __FILE__ ) ) )
 11    return;
 12 
 13  /*
 14   * get the original post id
 15   */
 16  $post_id = (isset($_GET['post']) ? absint( $_GET['post'] ) : absint( $_POST['post'] ) );
 17  /*
 18   * and all the original post data then
 19   */
 20  $post = get_post( $post_id );
 21 
 22  /*
 23   * if you don't want current user to be the new post author,
 24   * then change next couple of lines to this: $new_post_author = $post->post_author;
 25   */
 26  $current_user = wp_get_current_user();
 27  $new_post_author = $current_user->ID;
 28 
 29  /*
 30   * if post data exists, create the post duplicate
 31   */
 32  if (isset( $post ) && $post != null) {
 33 
 34    /*
 35     * new post data array
 36     */
 37    $args = array(
 38      'comment_status' => $post->comment_status,
 39      'ping_status'    => $post->ping_status,
 40      'post_author'    => $new_post_author,
 41      'post_content'   => $post->post_content,
 42      'post_excerpt'   => $post->post_excerpt,
 43      'post_name'      => $post->post_name,
 44      'post_parent'    => $post->post_parent,
 45      'post_password'  => $post->post_password,
 46      'post_status'    => 'draft',
 47      'post_title'     => $post->post_title,
 48      'post_type'      => $post->post_type,
 49      'to_ping'        => $post->to_ping,
 50      'menu_order'     => $post->menu_order
 51    );
 52 
 53    /*
 54     * insert the post by wp_insert_post() function
 55     */
 56    $new_post_id = wp_insert_post( $args );
 57 
 58    /*
 59     * get all current post terms ad set them to the new post draft
 60     */
 61    $taxonomies = get_object_taxonomies($post->post_type); // returns array of taxonomy names for post type, ex array("category", "post_tag");
 62    foreach ($taxonomies as $taxonomy) {
 63      $post_terms = wp_get_object_terms($post_id, $taxonomy, array('fields' => 'slugs'));
 64      wp_set_object_terms($new_post_id, $post_terms, $taxonomy, false);
 65    }
 66 
 67    /*
 68     * duplicate all post meta just in two SQL queries
 69     */
 70    $post_meta_infos = $wpdb->get_results("SELECT meta_key, meta_value FROM $wpdb->postmeta WHERE post_id=$post_id");
 71    if (count($post_meta_infos)!=0) {
 72      $sql_query = "INSERT INTO $wpdb->postmeta (post_id, meta_key, meta_value) ";
 73      foreach ($post_meta_infos as $meta_info) {
 74        $meta_key = $meta_info->meta_key;
 75        if( $meta_key == '_wp_old_slug' ) continue;
 76        $meta_value = addslashes($meta_info->meta_value);
 77        $sql_query_sel[]= "SELECT $new_post_id, '$meta_key', '$meta_value'";
 78      }
 79      $sql_query.= implode(" UNION ALL ", $sql_query_sel);
 80      $wpdb->query($sql_query);
 81    }
 82 
 83 
 84    /*
 85     * finally, redirect to the edit post screen for the new draft
 86     */
 87    wp_redirect( admin_url( 'post.php?action=edit&post=' . $new_post_id ) );
 88    exit;
 89  } else {
 90    wp_die('Post creation failed, could not find original post: ' . $post_id);
 91  }
 92}
 93add_action( 'admin_action_rd_duplicate_post_as_draft', 'rd_duplicate_post_as_draft' );
 94 
 95/*
 96 * Add the duplicate link to action list for post_row_actions
 97 */
 98function rd_duplicate_post_link( $actions, $post ) {
 99  if (current_user_can('edit_posts')) {
100    $actions['duplicate'] = '<a href="' . wp_nonce_url('admin.php?action=rd_duplicate_post_as_draft&post=' . $post->ID, basename(__FILE__), 'duplicate_nonce' ) . '" title="Duplicate this item" rel="permalink">Duplicate</a>';
101  }
102  return $actions;
103}
104 
105add_filter( 'post_row_actions', 'rd_duplicate_post_link', 10, 2 );