Find Argv[i] in /bin and /sbin in C - c

Question

I cannot locate argv[i] in /bin (or /sbin), package only checks the directory it was run from. How do I check for argv[i] in /bin and /sbin?
I am currently working on my own package manager and I am writing it in pure C. I am currently writing the check to see if the package(s) passed (using argv[]) are already installed. The issue I am having is that when I run for the check my code only checks in the directory it was run from and I need it to check /bin and /sbin (I am going to handle to checking of /sbin) and I am trying to get it to check /bin, but am having zero luck. I cannot seem to get this to work, each time they just check the current working directory and I need them to check /bin. I can't figure this out, has anyone by chance done this in pure C before? Thank you
These are all the methods I have tried so far, none of them work...
using stat()
#include <stdio.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <dirent.h>
int main(int argc, char *argv[])
{
struct dirent *de = calloc(1, sizeof(struct dirent));
DIR *dr = opendir("/bin"); /* directory to open */
short i;
struct stat *program = calloc(1, sizeof(struct stat));
if (dr == NULL) {
printf("directory could not be opened");
return 0;
}
while ((de = readdir(dr)) != NULL) {
for (i = 1; i < argc; i++) {
if (stat(argv[i], program) == 0) {
printf("found\n");
closedir(dr);
}
else {
printf("not found\n");
closedir(dr);
}
}
}
}
using realpath
#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
int main(int argc, char *argv[])
{
struct dirent *de = calloc(1, sizeof(struct dirent));
DIR *dr = opendir("/bin"); /* directory to open */
short i;
char *res = realpath(argv[i], NULL);
if (dr == NULL) {
printf("directory could not be opened");
return 0;
}
while ((de = readdir(dr)) != NULL) {
for (i = 1; i < argc; i++) {
if (res == NULL) {
printf("found\n");
closedir(dr);
}
else {
printf("not found\n");
closedir(dr);
}
}
}
}
using strcmp
#include <stdio.h>
#include <string.h>
#include <dirent.h>
int main(int argc, char *argv[])
{
struct dirent *de;
DIR *dr = opendir("/bin"); /* directory to open */
short i;
struct stat program;
if (dr == NULL) {
printf("directory could not be opened");
return 0;
}
while ((de = readdir(dr)) != NULL) {
for (i = 1; i < argc; i++) {
if (strcmp(de->d_name, argv[i]) == 0) {
printf("found\n");
closedir(dr);
}
else {
printf("not found\n");
closedir(dr);
}
}
}
}
I am expecting them all to work as follows:
check echo
// it would go to /bin and find echo and then print
found
but when I run them they only check the current working directory, so for example:
check connection.c
// finds connection.c in the same directory
found
Solution
Naha! I found a way to do it! So using the function chdir() I can run stat() in /bin like so:
#include <stdio.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
short i;
struct stat *program = calloc(1, sizeof(struct stat));
for (i = 1; i < argc; i++) {
chdir("/bin"); /* move to /bin */
if (chdir("/bin") != 0)
return 1;
if (stat(argv[i], program) == 0)
return 0;
else
return 1;
}
}

Answer 1

I tried simplifying your code just to output the contents of the folder, I get the contents of the '/bin' folder each time.
As a general rule of thumb, I like to get my code to compile without warnings, test it does what I expect it to, then work on the next bit.
The 'struct stat program' was causing the code not to compile, my guess is you were running an old version of the code.
#include <stdio.h>
#include <dirent.h>
#include <string.h>
int main(int argc, char *argv[])
{
struct dirent *de;
DIR *dr = opendir("/bin"); /* directory to open */
short i;
// struct stat program;
if (dr == NULL) {
printf("directory could not be opened");
return 0;
}
while ((de = readdir(dr)) != NULL) {
printf(de->d_name);
printf("\n");
}
}

Answer 2

If I understand you correctly then you’re confusing the semantics of opendir/readdir with those of chdir:
opendir does not change the working directory. This means that, e.g. realpath("echo", resolved_path) won’t resolve echo as /bin/echo but as $PWD/echo (where $PWD is the environment variable holding your current working directory).
That said, as a general rule you should not chdir inside your process. Instead, you can construct the path explicitly … e.g. via sprintf:
const char *binpath = "/bin";
char *fullpath = malloc(strlen(binpath) + 1 + strlen(argv[1]) + 1);
sprintf(fullpath, "%s/%s", binpath, argv[1]);
… and then stat the result (no need to dynamically allocate your struct stat either):
struct stat st;
if (stat(fullpath, &st) != 0) {
fprintf(stderr, "error in stat(): %s", strerror(errno));
}
printf("%s has inode %ju\n", fullpath, (unsigned long) st.st_ino);