Finding count of files with specific extension using C language using sytem calls

Question

Using bash, I can find count the count of specific extensions of a file like jpg, mp4 etc. How can I achieve this using C language system calls? Any help to achieve this using C language system calls?

ls -lR /path/to/dir/*.jpg | wc -l

I mean to achieve this using C language with any system library functions available. With bash or any regex its possible but I wanna solve using C language — Sravan Likith, Dec 05 '16 at 18:13
Possible duplicate of [C: Run a System Command and Get Output?](http://stackoverflow.com/questions/646241/c-run-a-system-command-and-get-output) — Jack Deeth, Dec 05 '16 at 18:13
It depends a bit on your definition of 'system call', but you might want any or all of [`scandir()`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/scandir.html) and friends, [`readdir()`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/readdir.html) and friends, [`nftw()`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/nftw.html), [`fnmatch()`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/fnmatch.html). — Jonathan Leffler, Dec 05 '16 at 18:16
@JonathanLeffler none of which are actually `c`, but rather POSIX... — EOF, Dec 05 '16 at 18:16
@EOF: Yes, but then there are very few system calls in Standard C; there are only library functions, and at least some of those I mentioned are more library function than system call. In fact, only the `readdir()` collection are really close to system calls in my understanding of the terminology. The rest are library functions built atop other system calls (in particular, atop `readdir()` et al). — Jonathan Leffler, Dec 05 '16 at 18:18
@JonathanLeffler: Well, on Linux `readdir()` is actually using the `getdents()` syscall AFAIK. Either way, it's unclear whether the OP wants to use `system()` or the BSD extension `syscall()` or whatever. — EOF, Dec 05 '16 at 18:20

BLUEPIXY · Answer 1 · 2016-12-06T05:27:16.853

1

Use popen like this.

#include <stdio.h>

int main(void){
    FILE *fp = popen("ls -lR /path/to/dir/*.jpg | wc -l", "r");
    int count;

    fscanf(fp, "%d", &count);
    pclose(fp);

    printf("%d\n", count);

    return 0;
}

edited Dec 06 '16 at 05:27

answered Dec 05 '16 at 18:30

BLUEPIXY

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@alk Thanks. fixed. – BLUEPIXY Dec 06 '16 at 05:27

score 1 · Answer 2 · answered Dec 05 '16 at 18:31

I code for general use. You can manipulate d_name on your own.

#include <sys/types.h>
#include <dirent.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
    DIR *dp;
    struct dirent *dirp;

    if (argc != 2)
        /* redo input */
    if ((dp = opendir(argv[1])) == NULL)
        /* error opening dir */
    printf("%8s %8s %8s %8s %8s\n",
            "d_name", "d_fileno",
            "d_reclen", "d_type",
            "d_namlen");
    while ((dirp = readdir(dp)) != NULL)
        printf("%8s %8d %8d %8d %8d\n",
                dirp->d_name, dirp->d_fileno,
                dirp->d_reclen, dirp->d_type,
                dirp->d_namlen);
    closedir(dp);
    return 0;
}

score 0 · Answer 3 · answered Dec 05 '16 at 18:28

0

Here is an example that shows how to using the readdir() function. You should be able to easily modify this to do what you want.

answered Dec 05 '16 at 18:28

Chimera

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Does that include the possibility this person is trying to avoid learning something and *still* pass an exam? – Jongware Dec 05 '16 at 18:33
1

Well, I gave this person an example they would have to modify to do what they needed. So they would have to learn or understand what the code is doing. – Chimera Dec 05 '16 at 18:35
@RadLexus: Yes, like Chimara said, my given code is only the guideline. He must modify my code to get his work done. – 郭春林 Dec 06 '16 at 06:49

Finding count of files with specific extension using C language using sytem calls

3 Answers3