Shell

This project is an implementation of a shell that runs as an application program on top of the Linux kernel. The shell accepts user commands (one line at a time) and executes them much like the default linux bash terminal.

Features Implemented

The following features have been implemented:

• Run an external command
• Run an external command by redirecting standard input/ output from/ to a file
• Combination of input and output redirection
• Run an external command in the background with possible input and output redirections
• Run several external commands in the pipe mode along with input and output redirections
• Interrupting commands running in your shell (Ctrl-C)
• Move a command in execution to the background (Ctrl-Z)
• Implementing cd and pwd
• Handling wildcards in commands (* and ?)
• Implementing searching through history using up/down arrow keys
• Implementing cursor movement using left/right arrow keys
• Cursor moves to start/end of line using Ctrl+A and Ctrl+E

I have tried to keep the shell as close to the bash terminal as possible, so the syntax of these commands are similar to their bash counterparts.

Additional Features

The following additional features have been implemented (not in normal BASH):

sb (squash bug):

Detects a simple malware process that spawns multiple child processes and remains in an idle state. The command creates a child process which identifies the parent, grandparent, and so on of the suspected process and suggests the root cause of the issue based on a heuristic. The heuristic is explained in the squashbug.heuristic.txt file. Usage: sb [-suggest] <pid>

delep (delete with extreme prejudice):

Helps to delete a file that has been locked by a process. The command takes a filepath as an argument, lists all the process pids which have the file open and those which are holding a lock over the file, and prompts the user to kill each of those processes. Usage: delep <filepath>

Note: For "sb" command, the squashbug.heuristic.txt file explains the heuristic used to detect the malware process.

Usage

To run the shell, run the following commands in the terminal:

1. Install readline library:

    sudo apt-get install libreadline-dev

2. Compile and run the shell:

    g++ shell.cpp -o shell -lreadline
    ./shell

Or, simply use the Makefile:

    sudo make
    ./shell