#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>  

int main(int argc, char *argv[]){
    if(argc < 2){
        fprintf(stderr, "Usage %s filename\n", argv[0]);
        return 1;
    }

    int f1 = open(argv[1], O_WRONLY | O_CREAT | O_APPEND, 0644);
    //int f1 = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644);
    if (f1 < 0) {
        //fprintf(stderr, "Could not open file (code %d)\n", errno);
        perror("Open");
        return 1;
    }
    write(f1, "Hello!\n", 7);

    close(f1);
    return 0;
}