Link ID in wordpress url

Ok. Here is your code. I just override default walker of wordpress. Please focus on text #header in this code.

If you worry about this code. So you can go to file: ...wp-includes/post-template.php at line 1238. It same code but I have add #header after get_permalink().

Hope that help.

 class WPSE_HasHeader_Custom_Walker extends Walker_Page {        function start_el( &$output, $page, $depth = 0, $args = array(), $current_page = 0 ) {            if ( $depth )                $indent = str_repeat("\t", $depth);            else                $indent = '';            extract($args, EXTR_SKIP);            $css_class = array('page_item', 'page-item-'.$page->ID);            if( isset( $args['pages_with_children'][ $page->ID ] ) )                $css_class[] = 'page_item_has_children';            if ( !empty($current_page) ) {                $_current_page = get_post( $current_page );                if ( in_array( $page->ID, $_current_page->ancestors ) )                    $css_class[] = 'current_page_ancestor';                if ( $page->ID == $current_page )                    $css_class[] = 'current_page_item';                elseif ( $_current_page && $page->ID == $_current_page->post_parent )                    $css_class[] = 'current_page_parent';            } elseif ( $page->ID == get_option('page_for_posts') ) {                $css_class[] = 'current_page_parent';            }            $css_class = implode( ' ', apply_filters( 'page_css_class', $css_class, $page, $depth, $args, $current_page ) );            if ( '' === $page->post_title )                $page->post_title = sprintf( __( '#%d (no title)' ), $page->ID );            /** CHANGE LINK HERE **/            $output .= $indent . '<li class="' . $css_class . '"><a href="' . get_permalink($page->ID) . '#header">' . $link_before . apply_filters( 'the_title', $page->post_title, $page->ID ) . $link_after . '</a>';            if ( !empty($show_date) ) {                if ( 'modified' == $show_date )                    $time = $page->post_modified;                else                    $time = $page->post_date;                $output .= " " . mysql2date($date_format, $time);            }        }    }    wp_list_pages(array(        'sort_column' => 'menu_order',        'title_li'    => '',        'echo'        => 1,        'walker' => new WPSE_HasHeader_Custom_Walker()    ));

Updated:

The second way:Thanks Mere Development. I thinks this is same idea with him but it much more simple in your case. Like this:

$link = wp_list_pages(array(                        'sort_column' => 'menu_order',                        'title_li'    => '',                        'echo'        => 0,                    ));echo preg_replace('/<a(.*)href="([^"]*)"(.*)>/', '<a$1href="$2#header"$3>', $link);

Christian's answer is great, and it got me thinking about alternative ways to do this, especially ones that allow you to use your wp_page_menu() function as originally requested. So here's another approach using a filter.

Add this function before your wp_page_menu() call, or in functions.php

function wp_list_pages_addhash($output) {    $dom = new DOMDocument;    $dom->loadHTML($output);    $links = $dom->getElementsByTagName('a');    foreach ($links as $link) {      $link->setAttribute('href', $link->getAttribute('href') . '#header');    }    $output = $dom->saveHTML();    return $output;}add_filter('wp_list_pages', 'wp_list_pages_addhash');

Then use your wp_page_menu call as you were originally in your theme:

wp_page_menu();

Explanation: It finds every href attribute of every link in the output of wp_list_pages and adds '#header' to the end. wp_page_menu in turn uses wp_list_pages to create output.