#include <string>
#include <vector>
#include <algorithm>
#include <iterator>
#include <iostream>
#include <sstream>
#include <cstdlib>
#include <cerrno>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

void checkFinish()
{
  int status;
  pid_t pid = ::waitpid(-1, &status, WNOHANG);
  if (pid < 0 && errno != ECHILD)
    std::cerr << "Waitpid failed" << std::endl;
  else if (pid > 0)
    std::cout << "Process " << pid << " finished with status " << status << std::endl;
}

int main ()
{

  while (true)
  {
    std::string cmd;
    checkFinish();
    std::cout << "Enter cmd : ";
    std::getline(std::cin, cmd);

    if (cmd.empty())
    {
      checkFinish();
      continue;
    }

    int pid;

    pid=::fork();

    if (pid < 0)
    {
      // error
      std::cerr << "fork() failed" << std::endl;
      std::exit(EXIT_FAILURE);
    }
    else if (pid > 0)
    {
      // we are parent
      std::cout << "Started pid " << pid << std::endl;
    }
    else
    {
      // break up string
      std::istringstream iss(cmd);
      std::vector<std::string> tokens;
      std::copy(std::istream_iterator<std::string>(iss),
          std::istream_iterator<std::string>(),
          std::back_inserter<std::vector<std::string> >(tokens));
      std::vector<const char*> raw;
      std::transform(tokens.begin(), tokens.end(),
          std::back_inserter<std::vector<const char*> >(raw),
          std::mem_fun_ref(&std::string::c_str));
      raw.push_back(0);
      ::execvp(raw[0], const_cast<char**>(&raw[0]));
      std::cerr << "Exec failed" << std::endl;
      std::exit(EXIT_FAILURE);
    }
    checkFinish();
  }
}