How to replace meta title and meta description in wordpress?

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

For anybody coming to this question in the future: This functionality can be accomplished using the Yoast SEO plugin.

However, if you do want to still do this yourself….

In order to modify the title, rather than the wp_head hook, you need to be using the filters that actually allow you to modify the title: wp_title

And you can / should use the wp_head in order to add the meta description (see the docs here: http://codex.wordpress.org/Meta_Tags_in_WordPress)

Also note there’s easier ways to get the page title, mentioned below…

For the title, your code would look something like so:

function changeTitle($title, $sep, $seplocation){
    global $wpdb;

    // NOTE: This is the HARD way to get the page title, and is unreliable...
    $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;

    // NOTE: Why not get pagename this way?
    global $post;
    $pageName = $post->post_title;

    // or if you need the slug...
    $pageName = $post->post_slug;

    $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) ) {         
                $title = 'Browse  '.$pageName.' | Some txt title | mysite.com';                 
        }
    }

    return $title;
}

add_action( 'wp_title', 'changeTitle', 10, 3 );