posts-list-add-export.php

<?php
add_filter('views_edit-post', 'add_export_link');
function add_export_link( $views ){
    $views[] = sprintf(
        '<a href="%s">%s</a>',
        esc_attr(site_url('/wp-admin/export.php?download=true&content=posts')),
        __('Export')
    );
    return $views;
}