is_single()判断是否文章页

<?php
is_single( int|string|array $post = '' )
?>

/**
 * Is the query for an existing single post?
 *
 * Works for any post type, except attachments and pages
 *
 * If the $post parameter is specified, this function will additionally
 * check if the query is for one of the Posts specified.
 *
 * @see is_page()
 * @see is_singular()
 *
 * @since 1.5.0
 *
 * @global WP_Query $wp_query Global WP_Query instance.
 *
 * @param int|string|array $post Optional. Post ID, title, slug, or array of such. Default empty.
 * @return bool Whether the query is for an existing single post.
 */
function is_single( $post = '' ) {
	global $wp_query;
 
	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1' );
		return false;
	}
 
	return $wp_query->is_single( $post );
}

<?php
if(is_single()){
    echo "我只会在文章页显示";
}else
{
    echo "我只显示在非文章页";
}
?>

<?php
if(is_single(123)){
    echo "我只会在文章ID为123的页面显示";
}
?>