/* $begin cpfile2-ans */
#include "csapp.h"

int main(int argc, char **argv) 
{
    int n;
    rio_t rio;
    char buf[MAXLINE];

    if ((argc != 1) && (argc != 2) ) {
	fprintf(stderr, "usage: %s <infile>\n", argv[0]);
	exit(1);
    }

    if (argc == 2) {  
	int fd;
	if ((fd = Open(argv[1], O_RDONLY, 0)) < 0) {
	    fprintf(stderr, "Couldn't read %s\n", argv[1]);
	    exit(1);
	}
	Dup2(fd, STDIN_FILENO);
	Close(fd);
    }
	
    Rio_readinitb(&rio, STDIN_FILENO);
    while((n = Rio_readlineb(&rio, buf, MAXLINE)) != 0) 
	Rio_writen(STDOUT_FILENO, buf, n);
    exit(0);
}    
/* $end cpfile2-ans */