#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>

unsigned int n_flag;
unsigned int lines;
void cat(const int fd) {
	char buf[4024];
	ssize_t len;

	while ((len = read(fd, buf, sizeof(buf))) > 0) {
		for (ssize_t i = 0; i < len; i++) {
			if (((i > 0) ? buf[i - 1] == '\n' : 1) && n_flag)
				printf(" %d ", ++lines);

			printf("%c", buf[i]);
		}
	}
}

int main(const int argc, const char **argv) {
	int i;
	for (i = 1; i < argc; i++) {
		if (argv[i][0] != '-')
			break;

		else if (!strcmp(argv[i], "-n"))
			n_flag = 1;

		else if (!strcmp(argv[i], "--help")) {
			printf("cat [-n (numerate)] [file1 file2 ...]\n");
			return 0;
		}
	}

	if (i == argc)
		cat(STDIN_FILENO);

	else {
		for (; i < argc; i++) {
			int fd = open(argv[i], O_RDONLY);
			if (fd < 0) {
				fprintf(stderr, "cat: %s %s\n", argv[i], strerror(errno));
				return 1;
			}

			cat(fd);
			close(fd);
		}
	}

	return 0;
}