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0x16. C - Simple Shell


Description


This is a project of simple shell, which provides a basic but essential tool for interacting with

computer systems, and it serves as a foundation for more advanced shell programs.


General Objectives


  • Who designed and implemented the original Unix operating system
  • Who wrote the first version of the UNIX shell
  • Who invented the B programming language (the direct predecessor to the C programming language)
  • Who is Ken Thompson
  • How does a shell work
  • What is a pid and a ppid
  • How to manipulate the environment of the current process
  • What is the difference between a function and a system call
  • How to create processes
  • What are the three prototypes of main
  • How does the shell use the PATH to find the programs
  • How to execute another program with the execve system call
  • How to suspend the execution of a process until one of its children terminates
  • What is EOF / “end-of-file”?

Requirements


  • Allowed editors: vi, vim, emacs
  • All your files will be compiled on Ubuntu 20.04 LTS using gcc, using the options -Wall -Werror -Wextra -pedantic -std=gnu89
  • All your files should end with a new line
  • A README.md file, at the root of the folder of the project is mandatory
  • Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl
  • Your shell should not have any memory leaks
  • No more than 5 functions per file
  • All your header files should be include guarded
  • Use system calls only when you need to (why?)
  • Write a README with the description of your project
  • You should have an AUTHORS file at the root of your repository, listing all individuals having contributed content to the repository. Format, see Docker

Tasks


0. Betty would be proud

Write a beautiful code that passes the Betty checks

1. Simple shell 0.1

Write a UNIX command line interpreter.

  • Usage: simple_shell

Your Shell should:

  • Display a prompt and wait for the user to type a command. A command line always ends with a new line.
  • The prompt is displayed again each time a command has been executed.
  • The command lines are simple, no semicolons, no pipes, no redirections or any other advanced features.
  • The command lines are made only of one word. No arguments will be passed to programs.
  • If an executable cannot be found, print an error message and display the prompt again.
  • Handle errors.
  • You have to handle the “end of file” condition (Ctrl+D)

You don’t have to:

  • use the PATH
  • implement built-ins
  • handle special characters : ", ', `, \, *, &, #
  • be able to move the cursor
  • handle commands with arguments

execve will be the core part of your Shell, don’t forget to pass the environ to it…

2. Simple shell 0.2

Simple shell 0.1 +

  • Handle command lines with arguments

3. Simple shell 0.3

Simple shell 0.2 +

  • Handle the PATH
  • fork must not be called if the command doesn’t exist

4. Simple shell 0.4

Simple shell 0.3 +

  • Implement the exit built-in, that exits the shell
  • Usage: exit
  • You don’t have to handle any argument to the built-in exit

5. Simple shell 1.0

Simple shell 0.4 +

  • Implement the env built-in, that prints the current environment