Which shell will execute the cmd when popen is called

Question

First of all, forgive my awful english.....

This is the prototype

FILE *popen(const char* cmd_string, const char* type);

Here is my question, the book says that when popen function is called, it will call exec to get a shell to execute the cmd_string we give to popen, but I'm not sure which shell will exec get, so can anyone give me an answer?

Answer 1

Let's try and see:

$ cat test.c
#include <stdio.h>

int main() {

  FILE *fp;
  char var[5];

  fp = popen("echo $0", "r");
  fgets(var, 5, fp);
  printf("%s", var);
}
$ gcc -Wall test.c
$ ./a.out
sh