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

extern char **environ;

static int printvars(int len, char **names, char n_flag) {
	int ret = 0;

	for (int i = 0; i < len; i++) {
		char *val = getenv(names[i]);
		if (!val) {
			ret = 1;
			continue;
		}

		printf("%s%c", val, n_flag);
	}

	return ret;
}

int main(int argc, char **argv) {
	char n_flag = '\n';

	int opt;
	while ((opt = getopt(argc, argv, "0")) != -1) {
		switch (opt) {
			case 'n':
				n_flag = '\0';
				break;

			default:
				puts("printenv [var1 var2...]\n\t-0 NUL terminated output\n");
				return 0;
		}
	}

	argv += optind;
	argc -= optind;

	if (argc == 0) {
		while (*environ)
			printf("%s%c", *environ++, n_flag);
	}

	else
		return printvars(argc, argv, n_flag);

	return 0;
}