Question

write a program in c to mimic the “deluser” command on linux. this command will delete system user. it has to handle 2 files “passwd” and “shadow”. both these files will be in some folder specified by an environment variable pfile. the program has to take all arguments as command line arguments (refer man pages for the command line arguments).

Answer 1

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, char *argv[]) {
    char line_1[100], line_2[100];
    char data_1[100][100], data_2[100][100];
    FILE *PFILE;
    int length, i = 0, j = 0, counter = 0;
    int k = 0, l = 0;

    if ((PFILE = fopen("shadow", "r")) != NULL) {
        while (fgets(line_1, sizeof(line_1), PFILE)) {
            length = strlen(line_1);
            if (length > 0 && line_1[length - 1] == '\n')
                line_1[--length] = '\0';
            if (strcmp(line_1, argv[1]) == 0) {
                counter = i;
                ++i;
                continue;
            }

            strcat(line_1, "\n");
            strcpy(data_1[i], line_1);
            ++i;
        }
        fclose(PFILE);


        PFILE = fopen("shadow", "w");
        while (j < i) {
            fputs(data_1[j], PFILE);
            ++j;
        }
        fclose(PFILE);


        if ((PFILE = fopen("passwd", "r")) != NULL) {
            while (fgets(line_2, sizeof(line_2), PFILE)) {
                length = strlen(line_2);
                if (length > 0 && line_2[length - 1] == '\n')
                    line_2[--length] = '\0';
                if (counter == k) {
                    ++k;
                    continue;
                }


                strcat(line_2, "\n");
                strcpy(data_2[k], line_2);
                printf("%s", data_2[k]);
                ++k;

            }
            fclose(PFILE);


            PFILE = fopen("passwd", "w");
            while (l < k) {
                fputs(data_2[l], PFILE);
                ++l;

            }
            fclose(PFILE);
            printf("User %s was deleted.\n", argv[1]);


            return 0;
        } else {
            printf("File open error!");
            exit(1);

        }
    } else {
        printf("File open error!");

        exit(1);
    }
}