#include <stdio.h> 
#include <stdlib.h> 
#include <unistd.h> 
#include <sys/ioctl.h> 
 
int main(int argc, char **argv) 
{ 
int on; 
int led_no; 
int fd; 
if (argc != 3 || sscanf(argv[1], "%d", &led_no) != 1 || sscanf(argv[2],"%d", &on) != 1 || 
    on < 0 || on > 1 || led_no < 0 || led_no > 3) { 
fprintf(stderr, "Usage: leds led_no 0|1\n"); 
exit(1); 
} 
fd = open("/dev/led", 0); 
if (fd < 0) { 
perror("can not open device led"); 
exit(1); 
} 
ioctl(fd, on, led_no); 
close(fd); 
return 0; 
}