wordpress纯代码替代ALL-IN-ONE-SEO插件

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta http-equiv="content-language" content="zh-CN" />
<title><?php if ( is_home() ) {
bloginfo('name'); echo " - "; bloginfo('description');
} elseif ( is_category() ) {
single_cat_title(); echo " _ "; bloginfo('name');
} elseif (is_single() || is_page() ) {
single_post_title(); echo " _ "; bloginfo('name');
} elseif (is_search() ) {
echo "搜索结果"; echo " _ "; bloginfo('name');
} elseif (is_404() ) {
echo '页面未找到!';echo " _ "; bloginfo('name');;
} else {
wp_title('',true);
} ?></title>
<?php
if (is_home()) {
$description = "学做网站论坛是一个细致的零基础学习怎么做网站的平台，大家可以在这里学习到如何做网站的知识和教程";
$keywords = "学建网站";}
elseif (is_single()|| is_page()) {
$description1 = get_post_meta($post->ID, "description", true);
$description2 = mb_strimwidth(strip_tags(apply_filters('the_content', $post->post_content)), 0, 200, "…");
// 填写自定义字段description时显示自定义字段的内容，否则使用文章内容前200字作为描述
$description = $description1 ? $description1 : $description2;
// 填写自定义字段keywords时显示自定义字段的内容，否则使用文章tags作为关键词
$keywords = get_post_meta($post->ID, "keywords", true);
if($keywords == '') {
$tags = wp_get_post_tags($post->ID);
foreach ($tags as $tag ) {
$keywords = $keywords . $tag->name . ", ";
}
$keywords = rtrim($keywords, ', ');
}
}
elseif (is_category()) {
$description = category_description();
$keywords = single_cat_title('', false);
}
elseif (is_tag()){
$description = tag_description();
$keywords = single_tag_title('', false);
}
$description = trim(strip_tags($description));
$keywords = trim(strip_tags($keywords));
?>
<meta name="description" content="<?php echo $description; ?>" />
<meta name="keywords" content="<?php echo $keywords; ?>" />
<?php wp_head(); ?>