fd_set read_fds;
struct timeval tv;
while(1){
    tv.tv_sec = 3;
    tv.tv_usec = 0;
    FD_ZERO(&read_fds);
    FD_SET(0,&read_fds);
    FD_SET(pipelogin,&read_fds);
    nfd = select(1,&read_fds,NULL,NULL,&tv);
    if(nfd==0)
        printf("Waiting...");
    if(FD_ISSET(0,&read_fds))
        comandos();
    if(FD_ISSET(pipelogin,&read_fds))
        VerificaLogin(pipelogin);
}