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Cairo University

Faculty of Computers and Information, CS241: OS1 (SP) 2019/2020

Assignment #1 Command Line Interpreter

Purpose

An operating system interfaces with a user through a Command Line Interpreter (CLI). A CLI is a software module capable of interpreting textual commands coming either from the user’s keyboard or from a script file. A CLI is often referred to as a shell.

Description

In this assignment, you will write a Command Line Interpreter (CLI) for your operating system. Your CLI should prompt the user to enter the input through the keyboard. After a sequence of characters is entered followed by a return, the string is parsed and the indicated command(s) executed. The user is then again prompted for another command.

Your program implements some built-in commands**; the list of required commands is listed below.** This means that your program must implement these commands directly by using the system calls that implement them. Do not use exec to implement any of these commands. The exit command is also a special case: it should simply cause termination of your program.

For this assignment, the following are essential features for your work:

1. Your CLI should be written in Java
2. Your application should contain 2 major classes (Parser, Terminal).

// Interface for parser

public class Parser{

String[] args; // Will be filled by arguments extracted by parse method String cmd; // Will be filled by the command extracted by parse method // Returns true if it was able to parse user input correctly. Otherwise false

// In case of success, it should save the extracted command and arguments

// to args and cmd variables

// It should also print error messages in case of too few arguments for a commands

// eg. “cp requires 2 arguments”

public boolean parse(String input);

public String getCmd();

public String[] getArguments();

}

// Interface for Terminal

public class Terminal{

public void cp(String sourcePath, String destinationPath ); public void mv(String sourcePath, String destinationPath); public void rm(String sourcePath);

public void pwd();

public void cat(String[] paths);

// Add any other required command in the same structure….. }

3. Your CLI should be written in Java and as a task function (CLI commands maybe written as functions or tasks).
4. All commands and parameters should be entered from the keyboard and parsed by your program, verified, and then executed. If the user enters wrong command or bad parameters the program should print some error messages. For example, if the user writes mkdir, the program should response by an error message as the command mkdir should have one parameter.
5. Your program should handle different parameters for each command. For example, if the user writes cd C:/ then the program should change to directory C:/ in case of the current directory is D:/. On the other hand, if the user writes cd only then the program should change to default directory (defined in your program) which may be D:/
6. You should implement the following commands: cd, ls, cp, mv, rm, mkdir, rmdir, and cat.

Note: for the cat command, you only need to implement the case of one parameter; you are not required to implement the case of two parameters. For the mv command you are not required to implement the option part such: “rm –r folderName”.