Instructions

Extend your code from the ps$2-$simple shell assignment so that it also handles I$/$O redirection, allowing the standard output to be redirected to an output file. For example:

$\%$ shell.out cat $<$ input $>$ output$$

This command specifies that the input file will be used to read data, and the output will be directed to the specified output file instead of the terminal. $$To accomplish this, you will need to use the dup$2$ system call. Additionally, you should enhance the parser to recognize the $<$ and $>$ symbols. If these symbols are present, the parser should tie STDIN$\_$FILENO and STDOUT$\_$FILENO to the respective file descriptors.

For additional learning support to assist you in solving this assignment, please refer to the materials listed at the bottom of the page and to the 'Relevant External Materials' page on Canvas.

Submission: Commit the following to your GitHub repository:

Your source code.

a Makefile that compiles and runs your program efficiently.

a README file that details any dependencies and provides step$-$by$-$step instructions on using the Makefile to compile and run the program.

Code from ps$2-$ Simple Shell:

$/*$

Alena Fisher

$10/27/2024$

$*/$

#include $"../$include$/$SimpleShell$.$h$"$

using namespace std;

void SimpleShell::execute$($const vector& argv$)$

$\{$

int status;

pid$\_$t child;

$//$ Spawning a child process

child $=$ fork$()$;

$//$ Parent process portion

if $($child $>0)\{$

cout $<<"("<<$ getpid$()<<")$ : I am a parent process waiting..." $<<$ endl;

waitpid$($child$,$ &status, $0)$; $//$ Wait for child process to finish

cout $<<$ "Waiting complete" $<<$ endl;

$\}$

$//$ Child process portion

else if $($child $==0)\{$

cout $<<$ "I am a child executing a new environment" $<<$ endl;

$//$ Ensure there's at least one argument

if $($argv$.$empty$())\{$

cerr $<<$ "Error: No command to execute" $<<$ endl;

$\_$exit$(1)$;

$\}$

$//$ Prepare arguments for exec $($must end with nullptr$)$

vector args;

for $($const auto& arg : argv$)\{$

args.push$\_$back$($arg$.$c$\_$str$())$;

$\}$

args.push$\_$back$($nullptr$)$;

$/*$

$1.$ Execute the ls command. execvp is a function that replaces the current process image

with a new process image. In this case, it is the command stored in args$[0]$

$2.$ const$\_$cast is used to cast the vector from const char$*$ to char$*$ const$*$ because having 'char$*\text{'}$

is required by execvp for the second argument.

$3.$ args.data$()$ returns a pointer to the vector

$4.\text{'}==-1\text{'}$: $-1$ is returned after attempting to execute the command if it fails. If it fails,

a message is printed. After this the program exits $\text{'}\_$exit$(1)\text{'}$

$*/$

if$($execvp$($args$[0],$ const$\_$cast$($args$.$data$()))==-1)\{$

perror$("$exec failed"$)$;

$\_$exit$(1)$;

$\}$

$\}$

else $\{$

perror$("$fork failed"$)$; $//$ Error handling if fork fails

exit$(1)$;

$\}$

$\}$

void SimpleShell::parse$($const string& line, vector& tokens, const string& delimiter$)$

$\{$

size$\_$t start $=0$;

size$\_$t end $=0$;

while $(($end $=$ line.find$($delimiter$,$ start$))!=$ string::npos$)\{$

if $($end $!=$ start$)\{//$ Ignore empty tokens

tokens.push$\_$back$($line$.$substr$($start$,$ end $-$ start$))$;

$\}$

start $=$ end $+$ delimiter.length$()$;

$\}$

if $($start $<$ line.length$())\{//$ Add the last token

tokens.push$\_$back$($line$.$substr$($start$))$;

$\}$

$\}$

void SimpleShell::run$()$

$\{$

while $($true$)\{$

string line;

vector tokens;

$//$ Print the prompt

cout $<<"("<<$ getpid$()<<")\%"$;

$//$ Get input from the keyboard

if $(!$getline$($cin$,$ line$))\{$

break; $//$ Exit the shell if input fails $($e$.$g$.,$ EOF$)$

$\}$

$//$ Parse the input into tokens

parse$($line$,$ tokens, $"")$;

if $($tokens$.$empty$())\{$

continue; $//$ Skip empty input

$\}$

$//$ Execute the user command

execute$($tokens$)$;

$\}$

$\}$

int main$()$

$\{$

SimpleShell shell;

shell.run$()$; $//$ Start the shell loop

return $0$;

$\}$