Run given command at random time intervals

rundom.c

/*
 * rundom.c - Run given command at random time intervals
 * Copyright (c) 2014 Arkadiusz Bokowy
 *
 * This projected is licensed under the terms of the MIT license.
 *
 * Compilation:
 * gcc -Wall -Wextra -o rundom rundom.c
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <getopt.h>
#include <time.h>


/* Run given system command and wait for the process exit. */
static void runcommand(const char *cmd) {
	/* in case someone would like to use some fancy bash syntax,
	 * just pass the command to the standard system call */
	system(cmd);
}

/* Return uniform and random number within the given range [min, max). */
static unsigned int randrange(unsigned int min, unsigned int max) {
	int base_random = rand();  /* in [0, RAND_MAX] */
	if (base_random == RAND_MAX)
		return randrange(min, max);
	/* now guaranteed to be in [0, RAND_MAX) */
	int range = max - min;
	int remainder = RAND_MAX % range;
	int bucket = RAND_MAX / range;
	/* there are range buckets, plus one smaller interval within
	 * a remainder of RAND_MAX */
	if (base_random < RAND_MAX - remainder)
		return min + base_random / bucket;
	return randrange(min, max);
}

int main(int argc, char *argv[]) {

	int opt;
	struct option longopts[] = {
		{"help", no_argument, NULL, 'h'},
		{"background", no_argument, NULL, 'b'},
		{"startup-run", no_argument, NULL, 'r'},
		{"max-count", required_argument, NULL, 'c'},
		{"interval", required_argument, NULL, 'i'},
		{"deviation", required_argument, NULL, 'd'},
		{0, 0, 0, 0},
	};

	int background = 0;
	int startup = 0;
	int counter = -1;
	int interval = 60;
	int deviation = 30;

	while ((opt = getopt_long(argc, argv, "hbrc:i:d:", longopts, NULL)) != -1)
		switch (opt) {
		case 'h':
return_usage:
			printf("usage: %s [options] <command>\n"
					"  -b, --background\tfork to background after startup\n"
					"  -r, --startup-run\trun command on startup\n"
					"  -c, --max-count=NUM\texit after NUM intervals\n"
					"  -i, --interval=NUM\tinterval (NUM seconds)\n"
					"  -d, --deviation=NUM\tinterval deviation (NUM seconds)\n",
					argv[0]);
			return EXIT_SUCCESS;
		case 'b':
			background = 1;
			break;
		case 'r':
			startup = 1;
			break;
		case 'c':
			counter = atoi(optarg);
			break;
		case 'i':
			interval = atoi(optarg);
			break;
		case 'd':
			deviation = atoi(optarg);
			break;
		default:
			printf("Try `%s -h` for more informations.\n", argv[0]);
			return EXIT_FAILURE;
		}

	if (counter == 0) {
		printf("error: counter value must be != 0\n");
		return EXIT_FAILURE;
	}
	if (interval <= 0) {
		printf("error: interval value must be >= 1\n");
		return EXIT_FAILURE;
	}
	if (deviation <= 0) {
		printf("error: deviation value must be >= 1\n");
		return EXIT_FAILURE;
	}

	if (optind == argc)
		/* we want to run some command, don't we? */
		goto return_usage;

	/* initialize random number generator */
	srand(time(NULL));

	if (startup) {
		runcommand(argv[optind]);
		if (counter > 0)
			counter--;
	}

	if (background) {
		/* run main loop as a background process */
		if (fork() != 0)
			return EXIT_SUCCESS;
	}

	int correction = 0;
	while (counter) {
		time_t start = time(NULL);

		int sleeptime = correction + interval -
			deviation / 2 + randrange(0, deviation);
		if (sleeptime > 0)
			sleep(sleeptime);

		runcommand(argv[optind]);
		if (counter > 0)
			counter--;

		correction = interval - (time(NULL) - start);
	}

	return EXIT_SUCCESS;
}