CODEWITHSUNDEEP
c
Rapidturtle
Rapidturtle

Reputation: 247

How to know if a file is readable by other user in C?

I am using linux to make a simple web server. I want to know what functions I should use to get a file's right of readablity.

Upvotes: 1

Views: 1672

Answers (3)

Mariusz
Mariusz

Reputation: 369

You should use stat function, or fstat if you want to use file descriptor instead of path. 

#include <stdio.h>
#include <stdlib.h>  
#include <sys/stat.h>
int main()
{
    char *f = "test.ts";

    struct stat *buff = malloc(sizeof(struct stat));
    if (stat(f,buff) < 0)
    return 1;

    printf("Information for %s\n",f);

    printf("File Permissions: \t");
    printf( (S_ISDIR(buff->st_mode)) ? "d" : "-");
    printf( (buff->st_mode & S_IRUSR) ? "r" : "-");
    printf( (buff->st_mode & S_IWUSR) ? "w" : "-");
    printf( (buff->st_mode & S_IXUSR) ? "x" : "-");
    printf( (buff->st_mode & S_IRGRP) ? "r" : "-");
    printf( (buff->st_mode & S_IWGRP) ? "w" : "-");
    printf( (buff->st_mode & S_IXGRP) ? "x" : "-");
    printf( (buff->st_mode & S_IROTH) ? "r" : "-");
    printf( (buff->st_mode & S_IWOTH) ? "w" : "-");
    printf( (buff->st_mode & S_IXOTH) ? "x\n" : "-\n");

    return 0;
}

Upvotes: 1

user5076313
user5076313

Reputation: 

#include<stdio.h>
#include<sys/stat.h>
#include<stdlib.h>
int main(int argc, char *argv[])
{
int i=0;
struct stat buf;
char ptr[]="test.txt";
printf("%s: ",ptr);
if (stat(ptr, &buf) < 0)
{
perror("stat error\n");
return;
}
if(buf.st_mode & S_IROTH)
{
 printf("The Others have a read permission for file %s\n",ptr);
}
 exit(0);
}

In this above example gives others have a read permission or not for the file test.txt in current directory.

Using the following macros to check permissions for user and others and group.

S_IRWXU - Read, write and execute permissions for owner

S_IRUSR - Owner has read permission

S_IWUSR - Owner has write permission

S_IXUSR - Owner has execute permission

S_IRWXG - Read, write and execute permissions for group

S_IRGRP - Group has read permission

S_IWGRP - Group has write permission

S_IXGRP - Group has execute permission

S_IRWXO - Read, write and execute permissions for others

S_IROTH - Others have read permission

S_IWOTH - Others have write permission

S_IXOTH - Others have execute permission

Using the above macros to modify the code based on what you want in the if condition in the example(if(buf.st_mode & S_IROTH)).

Upvotes: 0

Rahul Tripathi
Rahul Tripathi

Reputation: 172628

You can try like this:

su username -c 'ls /long/dir/user/yourfilename'

or

su username -s /bin/sh -c 'ls /long/dir/user/yourfilename'

Upvotes: 0

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