execl не принимает аргумент из pipe (версия 2, обновленная)

#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <iostream>
/* Execute the command using this shell program.  */
#define SHELL "/bin/sh"
using namespace std;

int
my_system ()
{
  int status;
  pid_t pid;
 int p[2];
  pipe(p);
  pid = fork ();


  if (pid == 0)
    { //Read
      close(p[1]);
      close(STDIN_FILENO);
      /* This is the child process.  Execute the shell command. */
      dup2(p[0], STDIN_FILENO);

      string str;
      cin >> str;
      execl (SHELL, SHELL, "-c", str.c_str(), NULL);
      _exit (EXIT_FAILURE);
      close(p[0]);
    }
  else if (pid < 0)
    /* The fork failed.  Report failure.  */
    status = -1;
  else
    {
      close(p[0]);
      close(STDOUT_FILENO);
      dup2(p[1], STDOUT_FILENO);
      // close(p[1]);
      string s;
      getline(cin, s);
      cout << s;
      close(STDOUT_FILENO);

    /* This is the parent process.  Wait for the child to complete.  */
      //    if (waitpid (pid, &status, 0) != pid)
      //      status = -1;

    }
  return status;
}

int main()
{
  my_system();
}