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

void usage(void) {
	fputs("usage: nl [filename]\n", stderr);
}

int main(int argc, char *argv[]) {
	if (argc > 2) {
		usage();
		exit(2);
	}
	FILE *in;
	if (argc == 2) {
		in = fopen(argv[1], "r");
		if (!in) {
			fprintf(stderr, "nl: cannot open '%s'\n", argv[1]);
			exit(1);
		}
	}
	else
		in = stdin;

	int line = 1;
	int flag = 0;
	printf("%5d  ", line++);
	while (!feof(in)) {
		unsigned char c = fgetc(in);
		if (c == '\n' || c == '\r')
			flag = 1;
		else if (c != 0xff) {
			if (flag)
				printf("\n%5d  ", line++);
			flag = 0;
			putchar(c);
		}
	}
	putchar('\n');
}