404.php
archive.php
category.php
footer.php
functions.php
header.php
index.php
page.php
screenshot.jpg
search.php
sidebar.php
single.php
style.css

/*
Theme Name : 自作テンプレート名(英字)
*/

<?php
/*
Plugin Name: page404GO!!
Plugin URI: https://zip358.com/plugin/page404go.zip
Description: 404ページを任意のURLへ変換し遷移させる
Author: taoka toshiaki
Version: 1.0
Author URI: https://zip358.com/
*/
add_action( 'wp', function() {
    global $wp;
    $domain = get_option('domain404page')?get_option('domain404page'):"https://zip358.com/";
    if(is_404()){
        wp_redirect($domain.$wp->request);
        exit;
    }
 });
add_action('admin_menu','page404go_setting');
function page404go_setting(){
	add_options_page(
		'zip358.com：プラグイン',
		'404リダイレクト設定',
		'administrator',
		'page404go',
		function(){
            if(isset($_POST["domain404page"])){
                if(preg_match("/https?://.*/$/",$_POST["domain404page"])){
                    $url = $_POST["domain404page"];
                }elseif(preg_match("/https?://.*/",$_POST["domain404page"])){
                    $url = $_POST["domain404page"]."/";
                }else{
                    $url = "https://zip358.com/";
                }
                update_option('domain404page', wp_unslash($url));
            }
            ?>
            <form method="post" action="">
                <h2>リダイレクトドメイン指定</h2>
                <input type="text" style="width:350px" name="domain404page" value="<?=get_option('domain404page')?get_option('domain404page'):""?>" placeholder="https://zip358.com/">
                <?php submit_button(); ?>
            </form>
            <?php
        }
	);
}