How to replace meta title and meta description in wordpress?

Question

Sorry if my question was basic or stupid but please help me to solve this issue. I'm trying to change <title> and <meta name="description" > tags dynamically in wordpress. so this is what I tried in function.php file.

function changeMeta_2(){
    global $wpdb;
    $cur_url = $_SERVER['REQUEST_URI']; 
    $basename = pathinfo($cur_url);
    $ebasename = $basename['filename'];
    if(is_numeric($ebasename)) {
    $url = explode('/', $basename['dirname']);
    $basename = explode('.', $url[count($url)-2]);
    $ebasename = $basename[0];
    }
    $pageName = $ebasename;



    $arraylist_subcat  = array("car","bike","boat","xxxx","yyyy","zzz","mmmm");
    $arraylist_maincat = array("aus","ind","usa","uae");


    $category_id = get_term_by('slug',$pageName, 'category');   
    $category_parentid  = get_term_by('id', $category_id->parent, 'category');   
    $parent_slug =  $category_parentid->slug;



   if ( is_page()) {        
        if ( in_array($pageName,$arraylist_maincat) ) {         
                $metaTitle = 'Browse  '.$pageName.' | Some txt title | mysite.com';
                $metaDescription = 'some of custome blablaaaaa text description  '.$pageName.' some of custome blablaaaaa text description ';                               
                echo '<title>'.$metaTitle.'</title>';
                echo '<meta name="description" content="'.$metaDescription.'"/>';                   
        }
    }
}
add_action( 'wp_head', 'changeMeta_2' );

In the above code I'm trying to change the title tag and meta description for term id which are matching with array values (in_array condition).

Everything works fine, but problem is instead of override(replace) <title> tag is appending in head. Its not changing it appending. please someone help me to solve this issue.

Answer 1

How document title is generated has changed since Wordpress v4.4.0. Now wp_get_document_title dictates how title is generated:

/**
 * Displays title tag with content.
 *
 * @ignore
 * @since 4.1.0
 * @since 4.4.0 Improved title output replaced `wp_title()`.
 * @access private
 */
function _wp_render_title_tag() {
    if ( ! current_theme_supports( 'title-tag' ) ) {
        return;
    }

    echo '<title>' . wp_get_document_title() . '</title>' . "\n";
}

Here is the code from v5.4.2. Here are the filters you can use to manipulate title tag:

function wp_get_document_title() {
    /**
    * Filters the document title before it is generated.
    *
    * Passing a non-empty value will short-circuit wp_get_document_title(),
    * returning that value instead.
    *
    * @since 4.4.0
    *
    * @param string $title The document title. Default empty string.
    */
    $title = apply_filters( 'pre_get_document_title', '' );
    if ( ! empty( $title ) ) {
        return $title;
    }
    // --- snipped ---
    /**
    * Filters the separator for the document title.
    *
    * @since 4.4.0
    *
    * @param string $sep Document title separator. Default '-'.
    */
    $sep = apply_filters( 'document_title_separator', '-' );

    /**
    * Filters the parts of the document title.
    *
    * @since 4.4.0
    *
    * @param array $title {
    *     The document title parts.
    *
    *     @type string $title   Title of the viewed page.
    *     @type string $page    Optional. Page number if paginated.
    *     @type string $tagline Optional. Site description when on home page.
    *     @type string $site    Optional. Site title when not on home page.
    * }
    */
    $title = apply_filters( 'document_title_parts', $title );
    // --- snipped ---
    return $title;
}

So here are two ways you can do it.

First one uses pre_get_document_title filter which short-circuits the title generation and hence more performant if you are not going make changes on current title:

function custom_document_title( $title ) {
    return 'Here is the new title';
}
add_filter( 'pre_get_document_title', 'custom_document_title', 10 );

Second way uses document_title_separator and document_title_parts hooks for the title and the title seperator that are executed later in the function, after title is generated using functions like single_term_title or post_type_archive_title depending on the page and about to be outputted:

// Custom function should return a string
function custom_seperator( $sep ) {
   return '>';
}
add_filter( 'document_title_separator', 'custom_seperator', 10 );

// Custom function should return an array
function custom_html_title( $title ) {
   return array(
     'title' => 'Custom Title',
     'site'  => 'Custom Site'
    );
}
add_filter( 'document_title_parts', 'custom_html_title', 10 );