C - Simple Shell

A simple unix command interpreter built as a project for the ALX software engineering program.

Learning Objectives

At the end of this project, you are expected to be able to explain to anyone:

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”?

Code will be compiled this way:

$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89

Allowed system calls and functions

Functions: closedir, exit, fflush, free, getcwd, getline, isatty, malloc, opendir, readdir

System calls: access, chdir, close, execve, _exit, fork, getpid, kill, open read, signal, stat (__xstat), lstat (__lxstat), fstat (__fxstat), wait, waitpid, wait3, wait4, write

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]

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
	$