Question

I’ve been struggling with this simple linux shell for hours now, and for some reason I just can’t get the most basic thing working correctly. Something is seriously messed up with how I handle my input or something, because one example of how this shell doesn’t work is the mkdir command. It randomly won’t create a random directory I never tried to create, and every time I do create a directory it manages to create some other ones with random names I obviously didn’t create. Something is messed up and I just have no clue, because I’ve been outputting my final argument array and it looks fine from there. Can someone please take a look at this for me.

#include<stdlib.h>
#include<stdio.h>
#include<sys/types.h>
#include<string.h>
#include<unistd.h>
#include<sys/wait.h>


int main(int argc, char *argv[]){
while(1){
    char line[100], *temp, *split[15];
    int child_id;
    printf("$ ");
    fgets(line, sizeof(line), stdin);
    line[strlen(line)-1] = '\0';

    temp = strtok(line, " ");
    int i = 0;
    while(temp != NULL){
        split[i] = temp;
        temp = strtok(NULL, " ");
        i++;
    }

    char *args[i];
    int j;
    for(j = 0; j < i; j++){
        args[j] = split[j];
        printf("%s\n", args[j]);
    }
    child_id = fork();
    if(child_id == 0){
        execvp(args[0], args);
        exit(0);
    }else{
        wait(&child_id);
    }


  }

}

Answer 1

When using execvp(), the final element of the args array must be NULL (this tells the kernel where the list of command line arguments ends).

You should be able to do this by adding split[i] = NULL; after the strtok() loop (oh, and no need to copy the array to args as mentioned in the comment above, just use split).