copy.c

#include <stdlib.h>
#include <fcntl.h>
#include "error_functions.h"
#include "tlpi_hdr.h"

#ifndef BUF_SIZE
#define BUF_SIZE 1024
#endif

#define _GH_JENKINS 1

int main(int argc, char* argv[]) {
    int input_fd, output_fd, open_flags;
    mode_t file_perms;
    ssize_t num_read;
    char buf[BUF_SIZE];

    if (argc != 3 || strcmp(argv[1], "--help") == 0)
        usage_err("%s old-file new-file\n", argv[0]);

    /* Open input and output files */

    input_fd = open(argv[1], O_RDONLY);
    if (input_fd == -1)
        err_exit("opening file %s", argv[1]);

    open_flags = O_CREAT | O_WRONLY | O_APPEND;
    file_perms = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH; /* rw-rw-rw- */
    output_fd = open(argv[2], open_flags, file_perms);
    if (output_fd == -1)
        err_exit("opening file %s", argv[2]);

    /* Transfer data until we encounter end of input or an error */

    while ((num_read = read(input_fd, buf, BUF_SIZE)) > 0)
        if (write(output_fd, buf, num_read) != num_read)
            fatal("write() returned error or partial write occured");
    if (num_read == -1)
        err_exit("read");
    
    if (close(input_fd) == -1)
        err_exit("close inpuit");
    if (close(output_fd) == -1)
        err_exit("close output");

    exit(EXIT_SUCCESS);
}