In this assignment, you will write a simple UNIX shell that accepts user commands and then executes each command in a separate process. It is based on programming project $1$ in chapter $3$ of the textbook. A starter skeleton program "prog.cpp$"$ and Makefile are provided. Type make to build the executable prog$2,$ and type $./$prog$2$ to run it$.$

Read on the course website for more details and submission instructions. Complete all the required features and remove "TODO"s from the source code. It's OK to add additional helper functions but don't change the file name.

$/**$

$*$ Assignment $2$: Simple UNIX Shell

$*$ @file pcbtable.h

$*$ @author $???($TODO: your name$)$

$*$ @brief This is the main function of a simple UNIX Shell. You may add additional functions in this file for your implementation

$*$ @version $0\mathrm{.}1$

$*/$

$//$ You must complete the all parts marked as "TODO". Delete "TODO" after you are done.

$//$ Remember to add sufficient and clear comments to your code

#include

#include

#include

#include

#include

#include

#include

using namespace std;

#define MAX$\_$LINE $80//$ The maximum length command

$/**$

$*$ @brief parse out the command and arguments from the input command separated by spaces

$*$

$*$ @param command

$*$ @param args

$*$ @return int

$*/$

int parse$\_$command$($char command$[],$ char $*$args$[])$

$\{$

$//$ TODO: implement this function

$\}$

$//$ TODO: Add additional functions if you need

$/**$

$*$ @brief The main function of a simple UNIX Shell. You may add additional functions in this file for your implementation

$*$ @param argc The number of arguments

$*$ @param argv The array of arguments

$*$ @return The exit status of the program

$*/$

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

$\{$

char command$[$MAX$\_$LINE$]$; $//$ the command that was entered

char $*$args$[$MAX$\_$LINE $/2+1]$; $//$ hold parsed out command line arguments

int should$\_$run $=1$; $/*$ flag to determine when to exit program $*/$

$//$ TODO: Add additional variables for the implementation.

while $($should$\_$run$)$

$\{$

printf$("$osh$>")$;

fflush$($stdout$)$;

$//$ Read the input command

fgets$($command$,$ MAX$\_$LINE, stdin$)$;

$//$ Parse the input command

int num$\_$args $=$ parse$\_$command$($command$,$ args$)$;

$//$ TODO: Add your code for the implementation

$/**$

$*$ After reading user input, the steps are:

$*(1)$ fork a child process using fork$()$

$*(2)$ the child process will invoke execvp$()$

$*(3)$ parent will invoke wait$()$ unless command included &

$*/$

$\}$

return $0$;

$\}$