#include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <sys/socket.h>
  #include <netinet/in.h>
  
  int main (int argc, char *argv[])
  {
  	int s, len, o, port = 6666;
  	char buf[512];
  	struct sockaddr_in addr;
  	socklen_t addr_len = sizeof addr;
  
  	if (argc > 1)
  		port = atoi (argv[1]);
  
  	s = socket (PF_INET, SOCK_DGRAM, IPPROTO_UDP);
  
  	o = 1;
  	len = 4;
  	setsockopt (3, SOL_SOCKET, SO_REUSEADDR, &o, len);
  
  	addr.sin_family = AF_INET;
  	addr.sin_port = htons (port);
  	addr.sin_addr.s_addr = INADDR_ANY;	/* receive broadcasts */
  
  	bind (s, (struct sockaddr *) &addr, sizeof addr);
  
  	for (;;) {
  		len = recvfrom (s, buf, sizeof buf, 0, (struct sockaddr *) &addr, &addr_len);
  		if (len < 0)
  			break;
  		if (write (1, buf, len) != len)
  			fprintf(stderr, "WARNING: serial characters dropped
  ");
  	}
  
  	return 0;
  }