#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <strings.h>
#include <stdio.h>

#define MAX 1024


void err_quit(char *msge);

int main(int argc, char *argv[])
{
	char buffer[8];
	char dest[MAX], *exten;
	int fd_orig, fd_dest, n;
	char *name_orig= argv[1];
	char name_dest[32];

	if (argc!=2) {
		fprintf(stderr, "Modo uso: %s <archivo.txt>\n", argv[0]);
		return -1;
	}

	exten= rindex(name_orig, '.');
	if (strcmp(exten, ".txt"))
		err_quit("Solo archivos de txt plano");

	if ((fd_orig= open(name_orig, O_RDONLY))== -1)
		err_quit("Error al abrir origen");

	strcpy(name_dest, "cifrado-");
	strcat(name_dest, name_orig);

	if ((fd_dest= creat(name_dest, 0666))== -1)
		err_quit("Error al abrir destino");

	while (n= read(fd_orig, buffer, sizeof buffer))
		write(fd_dest, buffer, n);

	close(fd_dest);
	close(fd_orig);	

	return 0;
}

void err_quit(char *msge) {
	perror(msge);
	exit(EXIT_FAILURE);
}