#include<stdlib.h>                               
#include<stdio.h>
int main()
{
    printf("Running ps with system\n");
    int code = system("ps au");//新进程结束后，system函数才返回
    //int code = system("ps au");//system函数立即返回
    printf("%d\n",code);
    printf("ps Done\n");
    exit(0);
}

int execl(const char *path,const char *arg0,...,(char*)0);
int execlp(const char *file,const char *arg0,...,(char*)0);
int execle(const char *path,const char *arg0,...,(char*)0,char *const envp[]);
int execv(cosnt char *path,char *const argv[]);
int execvp(cosnt char *file,char *const argv[]);
int execve(cosnt char *path,char *const argv[],char *const envp[]);

#include<stdio.h>
int main()
{
  printf("Running ps with execlp\n");
  execlp("ps","ps","au",(char*)0);
  printf("ps done");
  exit(0);
}

#include<stdio.h>
#include<sys/types.h>
int main()
{
  pid_t pid = fork();
  switch(pid)
  {
    case -1:
      perror("fork failed");
      exit(1);
      break;
    case 0:
      printf("\n");
      execlp("ps","ps","au",0);
      break;
    default:
      printf("parent,ps done\n");
      break;
  }
  exit(0);
}

pid_t wait(int *stat_loc);
pid_t waitpid(pid_t pid,int *stat_loc,int options);

#include<wait.h>
#include<stdio.h>
#include<sys/types.h>
int main()
{
  pid_t pid = fork();
  int stat = 0;
  switch(pid)
  {
    case -1:
      perror("fork failed");
      exit(1);
      break;
    case 0:
      printf("\n");
      exit(0);
      break;
    default:
      pid = wait(&stat);
      printf("Child has finished:PID=%d\n",pid);
      printf("parent,ps done\n");
      break;
  }
  exit(0);
}

#include<wait.h>
#include<stdio.h>
#include<sys/types.h>
int main()
{
  pid_t pid = fork();
  int stat = 0;
  switch(pid)
  {
    case -1:
      perror("fork failed");
      exit(1);
      break;
    case 0:
      printf("\n");
      execlp("ps","ps","au",0);
      break;
    default:
      do
      {
        pid = waitpid(pid,&stat,WNOHANG);
        if(pid==0)
        {
          printf("parent do something else.\n");
          sleep(1);
        }
      }while(pid==0);
      printf("Child has finished:PID=%d\n",pid);
      printf("parent,ps done\n");
      break;
  }
  exit(0);
}