CRAZY SHELL (CRASH)

This series of Assignments are an attempt to design a custom SHELL for thw LINUX based environment. The code is written in C, and makes use of syscalls and/or manually implemented code for commands of the shell.

To see the aggregation of the project you can have a look at the Assignment3P1 folder.

Features

Features of the shell include :

1. Color based seperation of prompt-line, error-messages, directory, files and executable.
2. Implementation of pipes and Input-Output redirection.
3. Implementation of space and time efficient data-structures like stack and linked-list for commands for efficient execution.
4. The entire code-base is written in C Language with libraries used capable of running on any standard LINUX based OS.
5. Implementation of signals and its handling.
6. A feature that shows Smile :') on successful execution of command and frown :'( other-wise.
7. Ability to read, write and update environment-variables of the base OS / SHELL.
8. Process handling, including running a process in background, bringing it to foreground etc.
9. If input file doesnot exist during redirection, the smart shell makes stdin as default input.

Codebase

Programs implementing the commands

1. mainP.c -> contains the main program that runs the infinite loop taking prompt (also contains code for commands like echo and pwd
2. ls.c -> code for the ls command that lists out all the files of a specified directory. Implemented -a and -l flags and color coded names.
3. ls.h -> header file for ls.c
4. forktest.c -> contains code for running foreground and background child processes
5. forktest.h -> header file for forktest.c
6. cd.c -> contains code for changing directory (Not needed anymore)
7. cd.h -> header file for cd.c
8. hist.c -> contains code for saving/loading/displaying history.
9. hist.h -> header file for hist.c logfiles/history.log contains history from previous sessions stored. (atmost 20 lines)
10. pinfor.c -> contains code for displaying information of a process whose pid is given as arguments (pinfo command)
11. pinfor.h -> header file for pinfor.c
12. nightswatch.c -> contains code for nightswatch command
13. nightswatch.h -> header file for nightswatch.c

Data Structures implemented to enhance complexity

14. list.c -> implementation of linked list for history command
15. list.h -> header file for list.c
16. stack.c -> implementation of stack data structure for ls command
17. stack.h -> header file for stack.c

Makefiles and Scripts to compile the code

18. init(.sh) -> creates initial logfiles and compiles code for the first time
19. compile(.sh) -> script for compiling the shell
20. makefile -> to implement make command and create an executable named crash

Include-files and Constants for code modularity

21. includefiles.h -> includes #include command required in various scripts
22. constants.h -> includes constants used in code e.g. LIST_LEN is used to allocate memory to arrays, strings etc.

Compilation and usage - makefile compilation

Go to the folder with code and compile

$ make
$ ./crash

Compilation and usage - SHELL Compilation

$ ./compile.sh
$ ./crash

Assumptions and Important Details

1. The length of all commands, arrays and stacks are assumed to be 1000 in length. This is a reasonable assumption but can be increased if needed.
2. exit command should be used for exit so that history can be saved.To exit type :

<username@devicename:~/path> exit

3. Implementation of both newborn and interrupt in nightswatch.
4. To quit nightswatch we have to prompt by pressing q followed by return.
5. As a feature, it seemed wise to implement that echo doesnot take " " into account but does take "\t" into account (feature, not a bug).
6. All background processes need to be exitted and history saved, so shell will be exitted using exit command only.
7. The pinfo command is more compatible with Linux 5.4.0.45-generic and OS Ubuntu 20.04.1 LTS (Focal Fossa). This is just a precautionary assumption, and is not necessarily required for the proper working of the crash shell entirely.
8. Maximum number of parellal instruction that can be run is 1000 but can be changed by changing value of a constant which is LIST-LEN.
9. Interrupt exits to processes is regarded failure and is greeted with a frown

Starting the Shell

To start the shell, for the first time :

$ ./init.sh
$ ./crash

For subsequent changes and compilation

$ ./compile.sh
$ ./crash.sh

Created by

VARUL SRIVASTAVA

• Roll Number : 2019111015
• E-Mail : varul.srivastava@research.iiit.ac.in
• Website : Varul Srivastava | IIIT Hyderabad
• Github : https://github.com/vs666