Why is C stdout not returning "ls" command content?

Question

I have been working on a reverse shell (not for malicious uses) and have started to learn how to use the popen function and get the output using stdout. I have started to test it out, and it was working fine, until I tried using the terminal command "ls". Could anyone point out (what I'm assuming is) my error and show me how to fix it?

Here is the code for the C program:

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

int main(){
    while (1){
        char* command = (char *) malloc(15*sizeof(char));
        char* output = (char *) malloc(2048);
        printf(">> ");
        scanf("%s", command);
        FILE* cmd = popen(command, "r");
        fputs(output, stdout);
        pclose(cmd);
        if (strlen(output) != 0){
            printf("\n%s\n", output);
        }
    }
}

and here is the code for the input I've provided the program, and it's result:

>> cd /Users/
sh: /Users/: is a directory //output from previous command
>> >> ls                    //also why did the program print '>>' twice?
>> 

Another question: Why did the program print >> twice?

Answer 1

The code appears to be missing the connection between popen() (really cmd) and the output variable. You could for example use fread() to read from the cmd "file" into output.

---

Calling scanf("%s", ...) will scan only one whitespace-separated word at a time. Your program is first running cd, then on the next iteration it is running /Users/.

---

The code is leaking memory by repeatedly allocating buffers command and output in the while loop without free-ing them.