Simple Shell

Background Context

Write a simple UNIX command interpreter.

It’s time for the famous Simple Shell project. This is one of the most anticipated project and also one that will challenge you a lot about everything you have learn so far:

Basics of programming
Basics of C
Basics of thinking like an engineer
Group work
and Learning how to learn

man or help:

sh (Run sh as well)

General

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

##General

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`

More Info

Output

Unless specified otherwise, your program must have the exact same output as sh (/bin/sh) as well as the exact same error output.

The only difference is when you print an error, the name of the program must be equivalent to your argv[0] (See below)

Example of error with sh:

	$ echo "qwerty" | /bin/sh
	/bin/sh: 1: qwerty: not found
	$ echo "qwerty" | /bin/../bin/sh
	/bin/../bin/sh: 1: qwerty: not found
	$

Same error with your program hsh:

	$ echo "qwerty" | ./hsh
	./hsh: 1: qwerty: not found
	$ echo "qwerty" | ./././hsh
	./././hsh: 1: qwerty: not found
	$

List of allowed functions and system calls

access (man 2 access)
chdir (man 2 chdir)
close (man 2 close)
closedir (man 3 closedir)
execve (man 2 execve)
exit (man 3 exit)
_exit (man 2 _exit)
fflush (man 3 fflush)
fork (man 2 fork)
free (man 3 free)
getcwd (man 3 getcwd)
getline (man 3 getline)
getpid (man 2 getpid)
isatty (man 3 isatty)
kill (man 2 kill)
malloc (man 3 malloc)
open (man 2 open)
opendir (man 3 opendir)
perror (man 3 perror)
read (man 2 read)
readdir (man 3 readdir)
signal (man 2 signal)
stat (__xstat) (man 2 stat)
lstat (__lxstat) (man 2 lstat)
fstat (__fxstat) (man 2 fstat)
strtok (man 3 strtok)
wait (man 2 wait)
waitpid (man 2 waitpid)
wait3 (man 2 wait3)
wait4 (man 2 wait4)
write (man 2 write)

Compilation

Your shell will be compiled this way:

gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh

Testing

Your shell should work like this in interactive mode:

	$ ./hsh
	($) /bin/ls
	hsh main.c shell.c
	($)
	($) exit
	$

But also in non-interactive mode:

	$ echo "/bin/ls" | ./hsh
	hsh main.c shell.c test_ls_2
	$
	$ cat test_ls_2
	/bin/ls
	/bin/ls
	$
	$ cat test_ls_2 | ./hsh
	hsh main.c shell.c test_ls_2
	hsh main.c shell.c test_ls_2
	$