README.md

README

24th September 2021

• Specifications
• Key features
• Constraints
• Instructions
• Mindmap/Overview
• Some specifications
• Examples of some functions

Specifications followed for minishell

• Works on LINUX
• Written using C++ (POSIX based system) using g++ 9.3.0 for Ubuntu
• MiniShell simulates bash and tries to include a reasonable subset of commands.

Key features included

Environment variables:

• printenv lists all environment variables.
• setenv
  (variable_name = variable_value)
  changes value of variable_name as per requirement.
• Any particular environment variable can be seen from writing the name of that variable or writing echo $VAR where VAR is variable name.(shown later too.)

Path functions: Most UNIX Commands are enterable.

Parsing

Piping

Input and Output redirection:

• Read mode, Write mode, Append mode

The following commands work flawlessly (internal+external)

however due to limitations of posix based compiler having access to the internal workings of an extended system,some natural functions which are internal to a shell but not to a C++ program may not work.Inspite of this, the following have been explicitly defined as internal commands to without using execvp and work perfectly:

1. help
2. cd
3. setenv *
4. exit (or quit or x)
5. history
6. printenv
7. clear
   *PLEASE NOTE : setenv works in the following format:
   setenv variable_name=new_variable_value
   If this is successful, you should get a "VALUE CHANGED" prompt and the same can be checked by writing the variable name in the terminal which will output the value of the environment variable.

Constraints for minishell

Single Level Piping only

On recognising piping, the command is executed directly

Single Level Redirection Only

On recognising piping, the command is executed directly,multi-level redirection is restricted.

No simultaneous Piping and Redirection

Redirection is checked for only if piping is not present

Instructions to run minishell

1. Compile with g++ or gnu post 9.2
2. Run with linux based OS

Overview points

1. The Shell boots up with the following screen giving developer credits and information and welcoming user to the shell.

Which clears and starts the shell after a delay of 4(max) seconds. The shell takes in input and produces corresponding output, in tandem with the flowchart defined for general systems. 2. The shell implements internal commands flawlessly and its details can be seen by typing help in the terminal. Most commands of UNIX work too. #### Main commands are : 1. man (example man man) displays manual 2. which 3. chsh 4. passwd 5. date 6. cal 7. clear 8. history 9. sleep 10. apropos 11. exit 12. shutdown 13. ls 14. cat 15. more 16. touch 17. mv 18. mkdir 19. rmdir 20. script 21. nano 22. find 23. touch 24. less 25. chmod 26. grep 27. printenv 28. getenv

Specifications to follow

• Blank Lines are handled quite well, they don’t get recorded in history.
• Redirection : MAKE SURE TO type both the command with no space before and after the redirection symbol (> , <, >>)
• Wrong commands give prompt to appropriate errors.
• setenv : type command as setenv (environment variable) = (new value) Make sure you use appropriate spacings.
• Exiting deletes history file(with exit or quit or x)

Examples

• help

* Environment variables output (all kinds)

* cd

* Input redirection,output redirection(write and append)

* History (the file is created in user’s tmp folder which MUST be present in all UNIX based systems)

* Exit

* Piping example