menu_t mainmenu = {
    3,
    (menuitem_t[]) {
        { "Catalog", MENU_DEFAULT, &catalog, 0, NULL },
        { "Screen 0", MENU_DEFAULT, NULL,
            3,
            (menuitem_t[]) {
                { "Screen 0", MENU_DEFAULT, &select_shell0, 0, NULL },
                { "Screen 1", MENU_DEFAULT, &select_shell1, 0, NULL },
                { "Screen 2", MENU_DEFAULT, &select_shell2, 0, NULL },
            }
        },
        { "System", MENU_DEFAULT | MENU_RIGHTALIGN, NULL,
            6,
            (menuitem_t[]) {
                { "Memory Management", MENU_DEFAULT, NULL, 0, NULL },
                { "OS Debugger",       MENU_DEFAULT, NULL, 0, NULL },
                { "Network Settings",  MENU_DEFAULT, NULL, 0, NULL },
                { "About",             MENU_DEFAULT, NULL, 0, NULL },
                { "Reboot",            MENU_DEFAULT, NULL, 0, NULL },
                { "Poweroff",          MENU_DEFAULT, NULL, 0, NULL },
            }
        },
    },
};

// ...
catalog_result = NULL;
menuitem_t *selection = menu_open(&mainmenu);
if(catalog_result != NULL)
{
    char const * str = catalog_result;
    while(*str) {
    putc(*str);
    currshell.input[currshell.cursor++] = *str++;
}
// ..