check-for-plugin-update

check-for-plugin-update.php

/* Check for updates */
function my_custom_update_checker() {
    $allowed_pages = array(
        'update-core',
        'plugins',
        'plugin-install',
        'network/update-core',
        'network/plugins',
        'network/plugin-install',
        'update'
    );

    add_action('current_screen', function($screen) use ($allowed_pages) {
        if (in_array($screen->id, $allowed_pages)) {
            my_update_checker(); /* The actual update function */
        }
    });
}
add_action('admin_init', 'my_custom_update_checker');