Filesystem

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <dirent.h>
#include <ctype.h>

int main(int argc, char **argv)
{
    const char *dname = (argc > 1 ? argv[1] : ".");
    DIR* pdir = opendir(dname);
    if(pdir == NULL) {
        perror("Can't open directory");
        return EXIT_FAILURE;
    }
    int textfiles=0;
    struct dirent* dent;
    while ((dent=readdir(pdir))!=NULL) {
        int d_name_len = strlen(dent->d_name);
        if (d_name_len > 4 &&
                strcmp(dent->d_name + (d_name_len - 4), ".txt") == 0) {
            textfiles++;
        }
    }
    printf("Number of text files: %i\n", textfiles);
    closedir(pdir);
    return 0;
}

#define _XOPEN_SOURCE 500
#include <stdlib.h>  /* for exit() */
#include <stdio.h>   /* for remove() */
#include <ftw.h>     /* for nftw() */

int unlink_cb(
    const char *fpath, const struct stat *sb, int typeflag, struct FTW *ftwbuf)
{
    return remove(fpath);
}

int rm_rf(const char *path)
{
    return nftw(path,
                unlink_cb,
                64 /* number of simultaneously opened fds, up to OPEN_MAX */,
                FTW_DEPTH | FTW_PHYS);
}

#include <stddef.h>   /* for offsetof() */
#include <stdlib.h>   /* for exit() */
#include <stdio.h>    /* for perror() */
#include <string.h>   /* for strcmp() */
#include <unistd.h>   /* for close(), unlink() */
#include <fcntl.h>    /* for open() */
#include <dirent.h>   /* for DIR */
#include <sys/stat.h> /* for stat */
#include <limits.h>   /* for NAME_MAX */

int rm_rf(const char* path)
{
    if (unlink(path) == 0) {
        return 0;
    } else {
        int dirfd = open(path, O_RDONLY | O_DIRECTORY);
        if (dirfd == -1) {
            perror("open");
            return -1;
        }
        if (rm_children(dirfd) == -1) {
            return -1;
        }
        if (rmdir(path) == -1) {
            perror("rmdir");
            return -1;
        }
        return 0;
    }
}

int rm_children(int dirfd)
{
    DIR* dir = fdopendir(dirfd);
    if (dir == NULL) {
        perror("fdopendir");
        if (close(dirfd) == -1) {
            perror("close");
        }
        return -1;
    }

    char buf[offsetof(struct dirent, d_name) + NAME_MAX + 1];

    struct dirent* dbuf = (struct dirent*)buf;
    struct dirent* dent = NULL;

    int ret = 0;

    for (;;) {
        if ((ret = readdir_r(dir, dbuf, &dent)) == -1) {
            perror("readdir_r");
            break;
        }
        if (dent == NULL) {
            break;
        }
        if (strcmp(dent->d_name, ".") == 0 || strcmp(dent->d_name, "..") == 0) {
            continue;
        }
        if ((ret = rm_at(dirfd, dent->d_name)) == -1) {
            break;
        }
    }

    if (closedir(dir) == -1) {
        perror("closedir");
        ret = -1;
    }

    return ret;
}

int rm_at(int dirfd, const char* name)
{
    int fd = openat(dirfd, name, O_RDONLY);
    if (fd == -1) {
        perror("openat");
        return -1;
    }

    int ret = 0;

    struct stat st;
    if ((ret = fstat(fd, &st)) == -1) {
        perror("fstat");
        goto out;
    }

    if (S_ISDIR(st.st_mode)) {
        ret = rm_children(fd);
        fd = -1;
        if (ret == -1) {
            goto out;
        }
    }

    ret = unlinkat(dirfd, name, S_ISDIR(st.st_mode) ? AT_REMOVEDIR : 0);
    if (ret == -1) {
        perror("unlinkat");
        goto out;
    }

out:
    if (fd != -1) {
        if (close(fd) == -1) {
            perror("close");
            ret = -1;
        }
    }

    return ret;
}