a little timer. "usage: timer [-f s] [-r s] -c shell-command\n\ -f s , timer expires once in s microseconds\n\ -r s, timer expires every s microseconds\n\ -c shell-command, execute this command via sh -c\n";

timer.c

#include <stdio.h>
#include <signal.h>
#include <sys/time.h>
#include <stdlib.h> 
#include <unistd.h> 
#include <errno.h>
#include <string.h>

#define CMDLEN 1024 

char command[CMDLEN]; 

char usage[] = "usage: timer [-f s] [-r s] -c shell-command\n\
		-f s , timer expires once in s microseconds\n\
		-r s,  timer expires every s microseconds\n\
		-c shell-command, execute this command via sh -c\n";

char nocmdmsg[] = "no command specified.";

int got_alarm = 0;

static void signal_handler(int sig)
{
	got_alarm = 1; 
}

int main(int argc, char **argv)
{ 
	extern char *optarg;
	struct sigaction sa;
	struct itimerval new;	
	struct itimerval old; 	
	int c = 0;
	int interval=0;
	int initial=0;
	int tosecond = 1000000;
	char *pc = &command[0];
	
	memset(command, '\x00', CMDLEN);
		
	if (argc < 4) {
		printf(usage);
		exit(0);
	}
	c = getopt(argc, argv, "f:r:c:h");
	while(c != -1) {
		switch (c) {
		case 'f':
			initial = atoi(optarg);
			if (initial < 0) {
				printf("-f s is not a number\n");
				return 0;
			}
			break;

		case 'r': 
			interval = atoi(optarg);
			if (interval < 0) { 
				printf("-r s is not a number\n");
				return 0;	
			}
			break;

		case 'c':
			memcpy(command, optarg, 8 * strlen(optarg));
			if (!command[0]) {
				pc = &nocmdmsg[0];
			}
			break;

		case 'h':
		case '?':
			printf(usage);
			return 0;

		} 
		c = getopt(argc, argv, "f:r:c:h"); 
	}


	new.it_interval.tv_sec = interval / tosecond;
	new.it_interval.tv_usec = interval % tosecond;
	if (initial == 0) {
		new.it_value.tv_sec = 0;
		new.it_value.tv_usec = 1;
	} else {
		new.it_value.tv_sec = initial / tosecond;
		new.it_value.tv_usec = initial % tosecond;
	}
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = 0;
	sa.sa_handler = signal_handler;

	if (sigaction(SIGALRM, &sa, NULL) == -1) {
		perror("sigaction");
		return 0;
	} 

	if (setitimer(ITIMER_REAL, &new, &old) < 0) {
		perror("setitimer");
		return 0;
	} 
	
	while(1) { 
		if (got_alarm == 1) { 
			printf("#%s\n", pc);
			system(command); 
			got_alarm = 0;
		}
		sleep(3600);
	} 
}