Simple mac changer.

mac_change.c

#include <assert.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <stdio.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/types.h>

int main(int argc, char** argv) {
    struct ifreq ifr;
    int s;
    char mac_char[] = "12:34:56:78:12:34";

    sscanf(mac_char,
           "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
           &ifr.ifr_hwaddr.sa_data[0],
           &ifr.ifr_hwaddr.sa_data[1],
           &ifr.ifr_hwaddr.sa_data[2],
           &ifr.ifr_hwaddr.sa_data[3],
           &ifr.ifr_hwaddr.sa_data[4],
           &ifr.ifr_hwaddr.sa_data[5]);

    s = socket(AF_INET, SOCK_DGRAM, 0);
    assert(s != -1);

    strcpy(ifr.ifr_name, "eth0");
    ifr.ifr_hwaddr.sa_family = ARPHRD_ETHER;
    assert(ioctl(s, SIOCSIFHWADDR, &ifr) != -1);

    return 0;
}