Adds and action in the WordPress admin to duplicate pages and posts

duplicate-posts.php

<?php

/**
 * Function creates post duplicate as a draft and redirects then to the edit post screen
 */
function duplicate_post_as_draft() {
    global $wpdb;

    if (!(isset($_GET['post']) || isset($_POST['post']) || (isset($_REQUEST['action']) && 'duplicate_post_as_draft' == $_REQUEST['action']))) {
        wp_die('No post to duplicate has been supplied!');
    }

    /* Get the original post id */
    $post_id = (isset($_GET['post']) ? absint($_GET['post']) : absint($_POST['post']));

    /* Get the original post data */
    $post = get_post($post_id);

    /* Set post author to current user */
    $current_user = wp_get_current_user();
    $new_post_author = $current_user->ID;

    /* If post data exists, create the post duplicate */
    if (isset($post) && $post != null) {

         /* Array of data to copy */
        $args = array(
            'comment_status' => $post->comment_status,
            'ping_status'    => $post->ping_status,
            'post_author'    => $new_post_author,
            'post_content'   => $post->post_content,
            'post_excerpt'   => $post->post_excerpt,
            'post_name'      => $post->post_name,
            'post_parent'    => $post->post_parent,
            'post_password'  => $post->post_password,
            'post_status'    => 'draft',
            'post_title'     => $post->post_title,
            'post_type'      => $post->post_type,
            'to_ping'        => $post->to_ping,
            'menu_order'     => $post->menu_order
        );

        /* Insert data into new post */
        $new_post_id = wp_insert_post($args);

        /* Get all current post terms and set them to the new post draft */
        $taxonomies = get_object_taxonomies($post->post_type);
        foreach ($taxonomies as $taxonomy) {
            $post_terms = wp_get_object_terms($post_id, $taxonomy, array('fields' => 'slugs'));
            wp_set_object_terms($new_post_id, $post_terms, $taxonomy, false);
        }

        /* Duplicate all post meta just in two SQL queries */
        $post_meta_info = $wpdb->get_results("SELECT meta_key, meta_value FROM $wpdb->postmeta WHERE post_id=$post_id");
        if (count($post_meta_info) != 0) {
            $sql_query = "INSERT INTO $wpdb->postmeta (post_id, meta_key, meta_value) ";
            foreach ($post_meta_info as $meta_info) {
                $meta_key = $meta_info->meta_key;
                $meta_value = addslashes($meta_info->meta_value);
                $sql_query_sel[]= "SELECT $new_post_id, '$meta_key', '$meta_value'";
            }
            $sql_query.= implode(" UNION ALL ", $sql_query_sel);
            $wpdb->query($sql_query);
        }

        /* Redirect to the edit post screen for the new draft */
        wp_redirect(admin_url('post.php?action=edit&post=' . $new_post_id));
        exit;
    } else {
        wp_die('Post duplication failed, could not find original post: ' . $post_id);
    }
}

add_action('admin_action_duplicate_post_as_draft', 'duplicate_post_as_draft');



/**
 * Add the duplicate link to action list for post_row_actions and page_row_actions
 * @param  [Array] $actions
 * @param  [Array] $post
 * @return [Array]
 */
function duplicate_post_link($actions, $post) {
    if (current_user_can('edit_posts')) {
        $actions['duplicate'] = '<a href="admin.php?action=duplicate_post_as_draft&amp;post=' . $post->ID . '" title="Duplicate this item" rel="permalink">Duplicate</a>';
    }

    return $actions;
}

add_filter('post_row_actions', 'duplicate_post_link', 10, 2);
add_filter('page_row_actions', 'duplicate_post_link', 10, 2);