Do I need to define more strtok functions? - c

Question

I want to run a command line argument to interpret a username, name, email, and home directory. I got the username part right but the rest is out of place. I don't know if I am placing the strtok function in the right place and each time I compile, it errors out "the variable is unused.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[]) {
if (argc != 2) {
printf("Usage: %s <username>\n", argv[0]);
return 1;
}
char *username = argv[1];
FILE *passwd = fopen("/etc/passwd", "r");
if (!passwd) {
perror("fopen");
return 1;
}
char *line = NULL;
size_t max_length = 0;
ssize_t ret_val = 0;
char line_copy[1000];
while ((ret_val = getline(&line, &max_length, passwd)) > 0) {
strncpy(line_copy, line, 999);
char *user = strtok(line_copy, ":");
if (strcmp(user, username) == 0) {
char *name = strtok(NULL, ":");
char *email = strtok(NULL, ":");
char *home_dir = strtok(NULL, ":");
printf("user: %s\n", user);
printf("name: %s\n", name);
printf("email: %s\n", email);
printf("home directory: %s\n", home_dir);
}
}
fclose(passwd);
passwd = NULL;
return 0;
}

Answer 1

At least on Linux /etc/passwd contains the colon separated fields login name, password, user id, group id, user name, home directory and shell. You have call strtok() for the fields you want to skip, and there is no email field:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int main(int argc, char *argv[]) {
if (argc != 2) {
printf("Usage: %s <username>\n", argv[0]);
return 1;
}
char *username = argv[1];
FILE *passwd = fopen("/etc/passwd", "r");
if (!passwd) {
perror("fopen");
return 1;
}
char *line = NULL;
size_t max_length = 0;
ssize_t ret_val;
while ((ret_val = getline(&line, &max_length, passwd)) > 0) {
if (strcmp(username, strtok(line, ":")) == 0) {
strtok(NULL, ":"); // password
strtok(NULL, ":"); // uid
strtok(NULL, ":"); // gid
char *name = strtok(NULL, ":");
char *home_dir = strtok(NULL, ":");
printf("user: %s\n", username);
printf("name: %s\n", name);
printf("home directory: %s\n", home_dir);
}
return 0;
}
fclose(passwd);
return 1;
}
Consider using getpwnam() instead:
#define _GNU_SOURCE
#include <pwd.h>
#include <stdio.h>
#include <sys/types.h>
int main(int argc, char *argv[]) {
if (argc != 2) {
printf("Usage: %s <username>\n", argv[0]);
return 1;
}
struct passwd *pw = getpwnam(argv[1]);
if(!pw)
return 1;
printf("user: %s\n", pw->pw_name);
printf("name: %s\n", pw->pw_gecos);
printf("home directory: %s\n", pw->pw_dir);
}