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#include <alloca.h>
#include <getopt.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <unistd.h>
static int print_id_objects();
static bool flag_print_uid = false;
static bool flag_print_gid = false;
static bool flag_print_name = false;
static bool flag_print_gid_all = false;
int main(int argc, char** argv)
{
static const char* valid_option_characters = "ugGn";
int opt;
while ((opt = getopt(argc, argv, valid_option_characters)) != -1) {
switch (opt) {
case 'u':
flag_print_uid = true;
break;
case 'g':
flag_print_gid = true;
break;
case 'G':
flag_print_gid_all = true;
break;
case 'n':
flag_print_name = true;
break;
default:
fprintf(stderr, "usage: id [-%s]\n", valid_option_characters);
return 1;
}
}
if (flag_print_uid + flag_print_gid + flag_print_gid_all > 1) {
fprintf(stderr, "cannot print \"only\" of more than one choice\n");
return 1;
}
int status = print_id_objects();
return status;
}
bool print_uid_object(uid_t uid)
{
if (flag_print_name) {
struct passwd* pw = getpwuid(uid);
printf("%s", pw ? pw->pw_name : "n/a");
} else
printf("%u", uid);
return true;
}
bool print_gid_object(gid_t gid)
{
if (flag_print_name) {
struct group* gr = getgrgid(gid);
printf("%s", gr ? gr->gr_name : "n/a");
} else
printf("%u", gid);
return true;
}
bool print_gid_list()
{
int extra_gid_count = getgroups(0, nullptr);
if (extra_gid_count) {
auto* extra_gids = (gid_t*)alloca(extra_gid_count * sizeof(gid_t));
int rc = getgroups(extra_gid_count, extra_gids);
if (rc < 0) {
perror("\ngetgroups");
return false;
}
for (int g = 0; g < extra_gid_count; ++g) {
auto* gr = getgrgid(extra_gids[g]);
if (flag_print_name && gr)
printf("%s", gr->gr_name);
else
printf("%u", extra_gids[g]);
if (g != extra_gid_count - 1)
printf(" ");
}
}
return true;
}
bool print_full_id_list()
{
uid_t uid = getuid();
gid_t gid = getgid();
struct passwd* pw = getpwuid(uid);
struct group* gr = getgrgid(gid);
printf("uid=%u(%s) gid=%u(%s)", uid, pw ? pw->pw_name : "n/a", gid, gr ? gr->gr_name : "n/a");
int extra_gid_count = getgroups(0, nullptr);
if (extra_gid_count) {
auto* extra_gids = (gid_t*)alloca(extra_gid_count * sizeof(gid_t));
int rc = getgroups(extra_gid_count, extra_gids);
if (rc < 0) {
perror("\ngetgroups");
return false;
}
printf(" groups=");
for (int g = 0; g < extra_gid_count; ++g) {
auto* gr = getgrgid(extra_gids[g]);
if (gr)
printf("%u(%s)", extra_gids[g], gr->gr_name);
else
printf("%u", extra_gids[g]);
if (g != extra_gid_count - 1)
printf(",");
}
}
return true;
}
int print_id_objects()
{
if (flag_print_uid) {
if (!print_uid_object(getuid()))
return 1;
} else if (flag_print_gid) {
if (!print_gid_object(getgid()))
return 1;
} else if (flag_print_gid_all) {
if (!print_gid_list())
return 1;
} else {
if (!print_full_id_list())
return 1;
}
printf("\n");
return 0;
}
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