// HW2.cpp : Defines the entry point for the console application.
//

#include <stdio.h>
#include <iostream>
#include <unistd.h>
#include <sys/types.h>
#include <fstream>
using namespace std;

int main(int argc, char* argv[])
{

	pid_t pid;
	pid_t mainPid;
	pid_t firstChild;
	pid_t secondChild;
	pid_t thirdChild;
	mainPid = getpid();

	// Fork 3 child processes

	pid = fork();
	firstChild = getpid();

	if (mainPid == getpid())
	{
		pid = fork();
		secondChild = getpid();
	}

	if (mainPid == getpid())
	{
		pid = fork();
		thirdChild = getpid();
	}

	// Parent process displays PID
	if (pid > 0)
	{
		cout << "This is the main process, my PID is " << getpid() << endl;
	}
	// One child process run "ls -l" command (using "execl" system call)
	if (pid == 0 && firstChild == getpid())
	{
		execl("/bin/ls", "ls", "-l", 0);
	}
	// Another child process run the "ps -ef"
	if (pid == 0 && secondChild == getpid())
	{
		execl("/bin/ps", "ps", "-ef", 0);
	}
	// The 3rd child process displays the content of the file. (use "more" or "cat")
	if (pid == 0 && thirdChild == getpid())
	{
		///////// This code section will open a local text file and display its contents////
		fstream fIn;
		fIn.open(argv[1], ios::in);

		if (fIn.is_open())
		{
			string s;
			while (getline(fIn, s))
			{
				cout << s << endl;

			}
			fIn.close();
		}
		else
			cout << "Error opening file " << endl;
		///////////////////////////////////////
	}
	//After all child processes terminate, the main process displays "main process terminates" then exits
	if (pid > 0)
	{
		wait(NULL);
		wait(NULL);
		wait(NULL);
		cout << "main process terminates" << endl;
	}


    return 0;
}