CAI - Assignment 1 – Command Line Interpreter - Solved

In this assignment, you will write a Command Line Interpreter (CLI) for your operating system.  

Your CLI should allow the user to enter the input through the keyboard. After the user writes the command and presses enter, the string is parsed, and the indicated command executed.  

The CLI will keep accepting different commands from the user until the user writes “exit”, then the CLI terminates.  

Your program structure and the list of required commands are listed below.  

Program Structure: 

Your program should contain 2 major classes: Parser & Terminal.

 
public class Terminal { 

   Parser parser; 

 

//Implement each command in a method, for example: 

public String pwd(){...} 

public void cd(String[] args){...}  // ... 

 

 

//This method will choose the suitable command method to be called public void chooseCommandAction(){...} 

 

public static void main(String[] args){...} } 
 

Required Commands: (You will choose only 12 commands to implement) 

Command Name 
What You Must Implement 
echo
Takes 1 argument and prints it.
pwd
Takes no arguments and prints the current path.
cd
Implement all these cases:

1.     cd takes no arguments and changes the current path to the path of your home directory.

2.     cd takes 1 argument which is “..” (e.g. cd ..) and changes the current directory to the previous directory.

3.     cd takes 1 argument which is either the full path or the relative (short) path and changes the current path to that path.
ls
Takes no arguments and lists the contents of the current directory sorted alphabetically.
ls -r
Takes no arguments and lists the contents of the current directory in reverse order.
mkdir
Takes 1 or more arguments and creates a directory for each argument. Each argument can be:

•      Directory name (in this case the new directory is created in the current directory)

•      Path (full/short) that ends with a directory name (in this case the new directory is created in the given path)
rmdir
Implement all these cases:

1.     rmdir takes 1 argument which is “*” (e.g. rmdir *) and removes all the empty directories in the current directory.

2.     rmdir takes 1 argument which is either the full path or the relative (short) path and removes the given directory only if it is empty.
touch
Takes 1 argument which is either the full path or the relative (short) path that ends with a file name and creates this file.
cp
Takes 2 arguments, both are files and copies the first onto the second.
cp -r
Takes 2 arguments, both are directories (empty or not) and copies the first directory (with all its content) into the second one. 
rm
Takes 1 argument which is a file name that exists in the current directory and removes this file.
cat
Takes 1 argument and prints the file’s content or takes 2 arguments and concatenates the content of the 2 files and prints it.
>
Format: command  > FileName

Redirects the output of the first command to be written to a file. If the file doesn’t exist, it will be created.  

If the file exists, its original content will be replaced.

Example: echo Hello World > myfile.txt ls > file 
>>
Like > but appends to the file if it exists.
Notes:  

•      You must implement the “exit” command which will allow the CLI to terminate.

•      If the user enters a wrong command or bad  parameters (invalid path, file instead of directory in certain commands, etc.), the program should print some error messages without terminating. 

•      You must handle all the mentioned cases in each command.

•      You can refer to the lab document for further information on the commands.


Sample Input & Output: