open_trait.c

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

int main(int argc, char **argv)
{
    struct stat s;
    int fd;
    int ret;

    if (argc != 3) {
        fprintf(stderr, "<%s> filename mode\n", argv[0]);
        fprintf(stderr, "mode is one of user, user_group, user_others\n");
        return -1;
    }

    mode_t mask = 0;

    mask = umask(mask);

    printf("creation of old mask %o\n", mask);

    mode_t mode = 0;

    if (!strcmp(argv[2], "user")) {
        mode = S_IRUSR | S_IWUSR;
    } else if (!strcmp(argv[2], "user_group")) {
        mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
    } else if (!strcmp(argv[2], "user_others")) {
        mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
    }

    if (mode == 0) {
        return -1;
    }

    printf("mode bits %o\n", mode);
    fd = open(argv[1], O_CREAT | O_WRONLY | O_TRUNC, mode);
    if (fd < 0) {
        return -1;
    }

    ret = stat(argv[1], &s);
    if (ret < 0) {
        return -1;
    }

    printf("file %s opened, mode %o\n", argv[1], s.st_mode & 0xfff);

    close(fd);
    return 0;
}