fgetgrent_r - Linux

Overview

fgetgrent_r() retrieves the next group entry from the group file (/etc/group) into a user-supplied buffer.

Syntax

int fgetgrent_r(FILE *file, struct group *grp, char *buf, size_t bufsize, struct group **result)

Options/Flags

None

Examples

Get Group Information for the Current User

#include <stdio.h>
#include <grp.h>

int main() {
  FILE *group_file = fopen("/etc/group", "r");
  struct group grp;
  char buf[1024];
  struct group *result;
  while (fgetgrent_r(group_file, &grp, buf, sizeof(buf), &result) == 0) {
    printf("%s\n", result->gr_name);
  }
  
  fclose(group_file);
  return 0;
}

Get Group Information for a Specific Group

#include <stdio.h>
#include <grp.h>

int main() {
  FILE *group_file = fopen("/etc/group", "r");
  char *group_name = "users";
  struct group grp;
  char buf[1024];
  struct group *result;
  while ((fgetgrent_r(group_file, &grp, buf, sizeof(buf), &result) == 0) && strcmp(grp.gr_name, group_name) != 0);
  if (result) {
    printf("%s\n", result->gr_name);
  } else {
    printf("Group not found\n");
  }
  fclose(group_file);
  return 0;
}

Common Issues

• Incorrect usage: Ensure all parameters are provided correctly and in the expected order.
• Invalid group file: Check the permissions of the /etc/group file and ensure it is a valid group file.
• Group not found: If the specified group name does not exist, fgetgrent_r() will return ENOENT.

Integration

• Can be used with other group-related functions such as getgrent(), getgrgid(), and getgrgid_r().
• Useful in scripting and automation for user and group management tasks.

Related Commands

• getgrent()
• getgrent_r()
• getgrgid()
• getgrgid_r()