/* File:  ~liux/public_html/courses/cop4610/examples/simple-pipe-cmd.cc
   Purpose: Demonstrate how to use pipes to communicate between
            parent and child processes and use dup for I/O redirection
   Author:  Xiuwen Liu, 
   On the web: 
     http://www.cs.fsu.edu/~liux/courses/cop4610/examples/simple-pipe-cmd.cc
   Compile:
     g++ -o simple-pipe-cmd simple-pipe-cmd.cc
*/

#include <sys/types.h>
#include <strings.h>
#include <sys/wait.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <iostream.h>
#define  MAXLINE  512

int main(int argc, char *argv[])
{
  int n, fd[2];
  pid_t  pid[2];
  char *my_argv[3];
  int status;
  if (pipe(fd) < 0) {
    perror("pipe");
    return -1;
  }
  
  if ( (pid[0] = fork()) < 0) {
    cerr << "Counld not create new process." << endl;
    perror("fork");
    return -1;
  }
  else {
    if (pid[0] ==0) { /* Child */
      close(0); dup(fd[0]); // Redict standard input fd[1]
      close(fd[0]); close(fd[1]); // Close unused open files
      if (argc ==3) {
	my_argv[0] = argv[2];
      }
      else {
	my_argv[0]= "/bin/cat";
      }
      my_argv[1] = (char *)NULL;
      if (execv(my_argv[0], my_argv) <0) {
	cerr << "Could not execute " << my_argv[0] << endl;
	exit(-1);
      }
    }
    else { /* Parent */
      if ( (pid[1]= fork()) < 0) {
	cerr << "Counld not create new process." << endl;
	perror("fork");
	return -1;
      }
      else {
	if (pid[1] ==0) {
	  close(1); dup(fd[1]); // Redict standard output to fd[0]
	  close(fd[0]); close(fd[1]); // Close unused open files
	  if (argc >= 2 ) {
	    my_argv[0]= argv[1];
	    my_argv[1] = (char *)NULL;
	  }
	  else {
	    my_argv[0]= "/bin/ps";
	    my_argv[1] = "-e";
	    my_argv[2] = (char *)NULL;
	  }
	  if (execv(my_argv[0], my_argv) <0) {
	    cerr << "Could not execute " << my_argv[0] << endl;
	    exit(-1);
	  }
	}
      }
    }
  }
  close(fd[0]); close(fd[1]); 
  waitpid(pid[0], &status, 0);
  waitpid(pid[1], &status, 0);
  return 0;
}