#include <stdio.h>

include <stdlib.h>
include <string.h>
include <errno.h>
include <unistd.h>
include <fcntl.h>
include <sys/types.h>
int main(int argc, char argv[])
{
    char buf = NULL;
    int fd_src = -1;
    int fd_dest = -1;
    int buf_size = 4096;
    int cnt = 0;
    struct flock lock;

if (argc < 3) {
    printf("usage: %s <src_file> <dest_file> [buf_size]\n", argv[0]);
    return 0;
}

if ((fd_src=open(argv[1], O_RDONLY)) == -1) {
    perror("open src. file");
    return 1;
}
if ((fd_dest=open(argv[2], O_WRONLY|O_CREAT|O_EXCL, 0664)) == -1) {
    perror("open dest. file");
    close(fd_src);
    return 2;
}
if (argc == 4) {
    buf_size = atoi(argv[3]);
}
buf = sbrk(buf_size);
if ((void*)-1 == buf) {
    perror("malloc");
    close(fd_src);
    close(fd_dest);
    return 3;
}

lock.l_type = F_RDLCK;
lock.l_whence = SEEK_SET;
lock.l_start = 0;
lock.l_len = 0;
lock.l_pid = -1;
if (fcntl(fd_src, F_SETLK, &lock) == -1) {
    fprintf(stderr, "%s has been locked by other process\n", argv[1]);
    close(fd_src);
    close(fd_dest);
    return 8;
}

errno = 0;
while ((cnt = read(fd_src, buf, buf_size)) > 0) {
    if (write(fd_dest, buf, cnt) < cnt) {
        perror("write");
        close(fd_src);
        close(fd_dest);
        return 4;
    }
}
if (0 != errno) {
    perror("read");
}
close(fd_src);
fd_src = -1;
close(fd_dest);
fd_dest = -1;
brk(buf);

return 0;

}</pre>