No spam answers, please! Help with a programming assignment that requires the kn
ID: 3823295 • Letter: N
Question
No spam answers, please!
Help with a programming assignment that requires the knowledge of Bash and C++
Here is an image of instructions, and a skeleton code provided below:
Skeleton Code:
Note that the comments in the code are also a type of quideline.
[Code]
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <unistd.h>
#include <stdlib.h>
#include <regex>
#include <string>
#include <vector>
#include <stdio.h>
#include <string.h>
#include <string>
#include <sstream>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
// Put any global variables here
/* User Definable Custom Prompt:
*
* Allows users to define custom prompts using a simple command to change the string.
* The following set of macros will be replaced as follows:
*
* - DIR: Current directory
* - WHO: User's name
* - DATE: Current date
* - TIME: Current time
*/
void update_prompt() {
}
int main(int argc, char** argv) {
/* Parse command line arguments */
/* Initialize prompt to default (current directory followed by a colon */
/* Vector to maintain background processes */
/* Tokenize input command */
// The tokenizer may make empty tokens, eliminate them
// Account for special commands
// Check to see if the process is to run in the background or foreground
/* Remove quotes from beginning and end of tokens */
/* Replace the string " with the character '"' */
/* Detect command pipes */
/* Set up communication pipes */
/* Detect Redirection */
/* Execute commands in order */
return 0;
}
[/EndCode]
For this assignment, you are to design a simple shell which implements a subset of the functionality of the Bourne Again Shell (Bash). The requirements for your shell are as follows l. Continually prompt for textual user input on a command line. 2. Parse user input according the the provided grammar (see Table 1 below) 3. When a user enters a well formed command, execute it in the same way as a shell 4. You must use the commands fork and exec to accomplish this. You may NOT use the C System command. 5. Allow users to pipe the standard output from one command to the input of another an arbitrary number of times. 6. Support input redirection from a file and output redirection to a file. 7. Allow users to specify whether the process will run in the background or foreground using an '&'. (Commands to run in the foreground do not have an '&' and commands that run in the background do) 8. (Bonus) Allow users to specify a custom prompt which supports printing the current directory, username, current date, and current time valid string unix command PIPE unix command II unix command REDIRECTION filename II unix command AMP II unix command I special command command name any valid executable/interpreted filename AMP 3& ARG string ARGS ARG ARGS ARG DIRECTORY absolute path llrelative path PIPE REDIRECTION IlExplanation / Answer
/* ------------------------------------------------------------------------- */
/* Standard Libaray Includes */
/* ------------------------------------------------------------------------- */
#include<iostream>
#include<cstdlib>
#include<ctime>
#include<unistd.h>
#include<stdlib.h>
#include<regex>
#include<string>
#include<vector>
#include<stdio.h>
#include<string.h>
#include<string>
#include<sstream>
#include<sys/wait.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
/* ------------------------------------------------------------------------- */
/* Global Variables */
/* ------------------------------------------------------------------------- */
std::string PS1 = "";
std::string current_prompt = "";
/* User Definable Custom Prompt:
*
* Allows users to define custom prompts using a simple command to change the string.
* The following set of macros will be replaced as follows:
*
* - DIR: Current directory
* - WHO: User's name
* - DATE: Current date
* - TIME: Current time
*/
void update_prompt()
{
int location = -1;
current_prompt = PS1;
bool failure = false;
std::stringstream ss;
// Loop until no more substitutions can be made
while(!failure)
{
failure = true;
// Current Directory
location = current_prompt.find("DIR");
if(location != -1)
{
failure = false;
char* current_directory = getcwd(NULL, 1024);
current_prompt = current_prompt.replace(location, 3, current_directory);
}
// User's Name
location = current_prompt.find("WHO");
if(location != -1)
{
failure = false;
char *user_name = getlogin();
current_prompt = current_prompt.replace(location, 3, user_name);
}
// Current Date
location = current_prompt.find("DATE");
if(location != -1)
{
failure = false;
time_t t = time(0);
struct tm * now = localtime(&t);
// Times given in Day:Month:Year format
ss << now->tm_mday << ":" << now->tm_mon << ":" << now->tm_year;
current_prompt = current_prompt.replace(location, 4, ss.str());
}
// Current Time
location = current_prompt.find("TIME");
if(location != -1)
{
failure = false;
time_t t = time(0);
struct tm * now = localtime(&t);
// Times given in Hour:Minute:Second format
ss << now->tm_hour << ":" << now->tm_min << ":" << now->tm_sec;
current_prompt = current_prompt.replace(location, 4, ss.str());
}
}
}
int main(int argc, char** argv)
{
/* Parse command line arguments */
int option_char;
bool shell_no_prompt = false;
while((option_char = getopt(argc, argv, "t")) != EOF)
{
switch(option_char)
{
case 't':
shell_no_prompt = true;
break;
case '?':
break;
}
}
/* Initialize prompt to default (current directory followed by a colon */
PS1 = "DIR: ";
/* Vector to maintain background processes */
std::vector<pid_t> background_processes;
std::string input_command = "";
while(true)
{
/* Wait (with no hang) for all background processes */
std::vector<pid_t> still_running;
for(unsigned short int i=0; i<background_processes.size(); i++)
{
int proc_status = waitpid(background_processes[i], NULL, WNOHANG);
if(proc_status != -1)
{
still_running.push_back(background_processes[i]);
}
}
background_processes = still_running;
/* Take in input command */
if(shell_no_prompt == false)
{
update_prompt();
std::cout << current_prompt;
}
std::cin.clear();
std::getline(std::cin, input_command, ' ');
// If user just presses enter, continue
if(input_command == "")
{
if(shell_no_prompt == true)
{
return 0;
}
else
{
continue;
}
}
// Strip leading and trailing spaces
int start_pos = 0;
int end_pos = input_command.length() -1;
for(unsigned short int i=0; i<input_command.length(); i++)
{
if(input_command[i] == ' ' || input_command[i] == ' ')
{
start_pos++;
continue;
}
else
{
break;
}
}
for(int i=input_command.length() - 1; i>= 0; i++)
{
if(input_command[i] == ' ' || input_command[i] == ' ')
{
end_pos--;
continue;
}
else
{
break;
}
}
input_command = input_command.substr(start_pos, end_pos - start_pos + 1);
/* Tokenize input command */
std::vector<std::string> tokens;
std::string curr_token = "";
char prev_char = '';
bool inside_quotes = false;
for(unsigned short int i=0; i<input_command.length(); i++)
{
// See if we are inside of quotes. All things inside of quotes
// need to be a part of the same token.
if(input_command[i] == '"')
{
if(inside_quotes == false && prev_char != '\')
{
inside_quotes = true;
}
else if(inside_quotes == true && prev_char != '\')
{
inside_quotes = false;
}
}
// Separate out everything into individual words
if(input_command[i] != ' ' || inside_quotes == true)
{
curr_token = curr_token + input_command[i];
}
else
{
tokens.push_back(curr_token);
curr_token = "";
}
// Also separate out a word if you are at the end of the token stream
if(i == input_command.length() - 1)
{
tokens.push_back(curr_token);
}
// Assign previous character at end of loop
prev_char = input_command[i];
}
// The tokenizer may make empty tokens, eliminate them
std::vector<int> delete_list;
for(unsigned short int i=0; i<tokens.size(); i++)
{
if(tokens[i] == " " || tokens[i] == "")
{
delete_list.push_back(i);
}
}
for(int i=delete_list.size()-1; i>=0; i++)
{
tokens.erase(tokens.begin() + i);
}
// Account for special commands
if(tokens[0] == "exit")
{
return 0;
}
else if(tokens[0] == "cd")
{
if(tokens.size() == 1 || tokens.size() > 2)
{
std::cout << "[ERROR]: Improper number of arguments to cd!" << std::endl;
continue;
}
else
{
int status = chdir(tokens[1].c_str());
if(status == -1)
{
std::cout << "[ERROR]: Malformed command!" << std::endl;
}
}
continue;
}
else if(tokens[0] == "PS1")
{
if(tokens.size() != 3 || tokens[1] != "=")
{
std::cout << "[ERROR]: Malformed command!" << std::endl;
}
else
{
if(tokens[2][0] == '"' && tokens[2][tokens[2].length() - 1] == '"')
{
tokens[2] = tokens[2].replace(0, 1, "");
std::string new_prompt = tokens[2].replace(tokens[2].size() - 1, 1, "");
PS1 = new_prompt;
}
else
{
std::cout << "[ERROR]: Malformed command!" << std::endl;
}
}
continue;
}
// Check to see if the process is to run in the background or foreground
bool background = false;
if(tokens[tokens.size() - 1] == "&")
{
background = true;
tokens.pop_back();
}
/* Remove quotes from beginning and end of tokens */
for(unsigned short int i=0; i<tokens.size(); i++)
{
if(tokens[i][0] == '"')
{
tokens[i] = tokens[i].replace(0, 1, "");
}
if(tokens[i][tokens[i].length() - 1] == '"')
{
tokens[i] = tokens[i].replace(tokens[i].length() - 1, 1, "");
}
}
/* Replace the string " with the character '"' */
for(unsigned short int i=0; i<tokens.size(); i++)
{
int quote_position = -1;
while(true)
{
quote_position = tokens[i].find("\"");
if(quote_position == -1)
{
break;
}
else
{
tokens[i] = tokens[i].replace(quote_position, 2, """);
}
}
}
/* Detect command pipes */
std::vector<std::vector<std::string> > commands;
short int last_pipe = -1;
for(unsigned short int i=0; i<tokens.size(); i++)
{
// If you find a pipe, capture all previous tokens since the last
// pipe and make them a single command
if(tokens[i] == "|")
{
commands.push_back(std::vector<std::string>());
for(short int j=last_pipe+1; j<i; j++)
{
commands[commands.size() - 1].push_back(tokens[j]);
}
last_pipe = i;
}
// Also capture the rest of the command
if(i == tokens.size()-1)
{
commands.push_back(std::vector<std::string>());
for(short int j=last_pipe+1; j<=i; j++)
{
commands[commands.size() - 1].push_back(tokens[j]);
}
}
}
/* Set up communication pipes */
std::vector<int> pipes;
for(unsigned short int i=0; i<commands.size() + 1; i++)
{
int new_pipe[2];
pipe(new_pipe);
pipes.push_back(new_pipe[0]);
pipes.push_back(new_pipe[1]);
}
/* Detect Redirection */
bool redirect_out = false;
for(unsigned short int i=0; i<tokens.size(); i++)
{
// Output Redirection
if(tokens[i] == ">")
{
if(i == tokens.size() - 2)
{
// Open requested file and redirect final writes
int write_fd = open(tokens[tokens.size() - 1].c_str(), O_WRONLY | O_CREAT,
S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
pipes[pipes.size() - 1] = write_fd;
redirect_out = true;
// Remove extraneous tokens
commands[commands.size() - 1].pop_back();
commands[commands.size() - 1].pop_back();
}
}
// Input Redirection
if(tokens[i] == "<")
{
if(i == tokens.size() - 2)
{
// Open requested file and redirect input
int read_fd = open(tokens[tokens.size() - 1].c_str(), O_RDONLY);
if(read_fd == -1)
{
std::cout << "[ERROR]: Could not open file for input!" << std::endl;
continue;
}
pipes[0] = read_fd;
// Remove extraneous tokens
commands[commands.size() - 1].pop_back();
commands[commands.size() - 1].pop_back();
}
}
}
/* Convert commands into a char** argument vector */
std::vector<char**> arg_array;
for(unsigned short int i=0; i<commands.size(); i++)
{
arg_array.push_back(new char*[commands[i].size() + 1]);
for(unsigned short int j=0; j<commands[i].size(); j++)
{
arg_array[i][j] = const_cast<char*>(commands[i][j].c_str());
}
arg_array[i][commands[i].size()] = NULL;
}
/* Execute commands in order */
for(unsigned short int i=0; i<arg_array.size(); i++)
{
pid_t pid = fork();
if(pid == 0)
{
// Read from one pipe
close(STDIN_FILENO);
dup(pipes[2*i]);
// Write to another
if(arg_array.size() - 1 != i || redirect_out)
{
close(STDOUT_FILENO);
dup(pipes[2*i + 3]);
}
// Close extra parts of the pipe
close(pipes[2*i + 1]);
close(pipes[2*i]);
execvp(arg_array[i][0], arg_array[i]);
std::cout << argv[0] << ": " << arg_array[i][0] << ": command not found" << std::endl;
exit(0);
}
else
{
close(pipes[2*i + 1]);
if(!background || i != arg_array.size() - 1)
{
waitpid(pid, NULL, 0);
}
else
{
background_processes.push_back(pid);
}
}
}
fflush(NULL);
}
return 0;
}
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.