• By Julien Barbier
• Project to be done in teams of 2 people (team: Awal Umar, Saddiq Dawuni Abubakari)

For this project, students are expected to look at these concepts:

• Everything you need to know to start coding your own shell
• Approaching a Project

Write a simple UNIX command interpreter.

^ "The Gates of Shell", by Spencer Cheng, featuring Julien Barbier

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

I would like to take this moment to remind you about a few important things. First, remember the framework. If you do not know it by heart already, it is probably a good idea to read it again: https://intranet.alxswe.com/concepts/559

Note that there is no point in this framework that says it is ok to look at code from other people. It is not allowed to look at other people’s code, either other students or online articles or videos. At ALX SE we do not copy solutions and we do not look at it when we start a project.

• NEVER copy any code, never look at solution (and never give any solution to your friends, you are not helping them by doing so)
• ALWAYS write code alone from scratch after you get help to check that you have actually understood. If you can not do it, you have not understood enough, and need to study more. Do not rewrite code from memory, but from understanding.

I saw some of you sharing resources with each other already. Tutorials on how to do the shell step by step with all the code associated with these, or even video and documents with the solution without even any explanation. This is not the right way to learn. Please do not be tempted by these links. They will only push you to take shortcuts and / or cheat. And trust me, you will be caught. Kimba is not a joke and he is here to remind you why you are here.

While we encourage the use of ChatGPT and co in the framework (also, not right away, but at the right step, see framework), it is important to understand that the same rules apply to these AI tools (again, in the context of learning. When you will work it will be completely different, but context matters). At no point does it say that you are allowed to use copilot or ChatGPT to code the solution. If you do, you will get 200% (for a few hours), understand 0, learn 0, and you will be caught for cheating 100%, and then your score for both you and your partner will be 0%. If you don’t get how to use ChatGPT and other AI tools in the context of learning, simply do not use them.

The reality is that at this point of the program, if you have not cheated before, you have everything you need to complete the project with what you have learned + the page “Everything you need to know to start coding your own shell” (https://intranet.alxswe.com/concepts/64)

Actually, you do not even need to open Google once. Focus on your whiteboarding, and everything will fall in place. Remember, at ALX SE you never learn the solution, you learn how to walk toward the solution. You learn to create the tutorial, so if you follow one, you are looking at the solution, you are taking a very serious shortcut that will undermine your learning.

Last thing about the framework. Note that the first thing to do is “0. Read”. Every detail counts. Make sure you read and test everything.

The shell project is a group project. That means you will be paired with someone. You already did this with printf, so please apply everything you have learned from the printf experience here. A quick reminder, that a group project is NOT:

In the context of learning (some of these will no longer be true when you work):

A group project at ALX SE is a project that both of you are responsible for. Everything anyone pushes to Github is the responsibility of both partners. It is not ok to say later “I didn’t cheat it’s my partner I didn’t know they didn’t tell me”.

So you are supposed to work TOGETHER. And you should both understand every single line of code that any of you pushes. Here is a link for you to read about pair programming: https://intranet.alxswe.com/concepts/121

If you plan on not working on the shell project (or if at any point in time you can’t), it is your responsibility to tell both the staff and your partner so that they can find another partner who will work with them asap.

• I do nothing and cross fingers for my partner to do everything so I can have a good score
• I do everything because I am so much better than my partner and I don’t care about them

If your group gets caught for plagiarism we will not tolerate “I didn’t do anything, so I should not be flagged”. Yes you should be flagged, because you are someone who doesn’t care about others and thought it was ok to let your partner down and to maybe get the score without doing anything.

The shell is an incredibly cool project. GL HF!

Julien

Read or watch:

• Unix shell
• Thompson shell
• Ken Thompson
• Everything you need to know to start coding your own shell concept page

man or help:

• sh (Run sh as well)

At the end of this project, you are expected to be able to explain to anyone, without the help of Google:

• 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"?

• 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?)

There should be one project repository per group. If you clone/fork/whatever a project repository with the same name before the second deadline, you risk a 0% score.

• 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
$

• 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)

Your shell will be compiled this way:

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

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
$

The Checker will be released at the end of the project (1-2 days before the deadline). We strongly encourage the entire class to work together to create a suite of checks covering both regular tests and edge cases for each task. See task 8\. Test suite.

mandatory

• Write a README
• Write a man for your shell.
• You should have an AUTHORS file at the root of your repository, listing all individuals having contributed content to the repository. Format, see Docker

Repo:

• GitHub repository: simple_shell
• File: README.md, man_1_simple_shell, AUTHORS

mandatory

Write a beautiful code that passes the Betty checks

Repo:

• GitHub repository: simple_shell

mandatory

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

julien@ubuntu:~/shell$ ./shell
#cisfun$ ls
./shell: No such file or directory
#cisfun$ /bin/ls
barbie_j       env-main.c  exec.c  fork.c  pid.c  ppid.c    prompt   prompt.c  shell.c  stat.c         wait
env-environ.c  exec    fork    mypid   ppid   printenv  promptc  shell     stat test_scripting.sh  wait.c
#cisfun$ /bin/ls -l
./shell: No such file or directory
#cisfun$ ^[[D^[[D^[[D
./shell: No such file or directory
#cisfun$ ^[[C^[[C^[[C^[[C
./shell: No such file or directory
#cisfun$ exit
./shell: No such file or directory
#cisfun$ ^C
julien@ubuntu:~/shell$ echo "/bin/ls" | ./shell
#cisfun$ barbie_j       env-main.c  exec.c  fork.c  pid.c  ppid.c    prompt   prompt.c  shell.c stat.c         wait
env-environ.c  exec    fork    mypid   ppid   printenv  promptc  shell     stat test_scripting.sh  wait.c
#cisfun$ julien@ubuntu:~/shell$

Repo:

• GitHub repository: simple_shell

mandatory

Simple shell 0.1 +

• Handle command lines with arguments

Repo:

• GitHub repository: simple_shell

mandatory

Simple shell 0.2 +

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

julien@ubuntu:~/shell$ ./shell_0.3
:) /bin/ls
barbie_j       env-main.c  exec.c  fork.c  pid.c  ppid.c    prompt   prompt.c  shell_0.3  stat    test_scripting.sh  wait.c
env-environ.c  exec    fork    mypid   ppid   printenv  promptc  shell     shell.c    stat.c  wait
:) ls
barbie_j       env-main.c  exec.c  fork.c  pid.c  ppid.c    prompt   prompt.c  shell_0.3  stat    test_scripting.sh  wait.c
env-environ.c  exec    fork    mypid   ppid   printenv  promptc  shell     shell.c    stat.c  wait
:) ls -l /tmp
total 20
-rw------- 1 julien julien    0 Dec  5 12:09 config-err-aAMZrR
drwx------ 3 root   root   4096 Dec  5 12:09 systemd-private-062a0eca7f2a44349733e78cb4abdff4-colord.service-V7DUzr
drwx------ 3 root   root   4096 Dec  5 12:09 systemd-private-062a0eca7f2a44349733e78cb4abdff4-rtkit-daemon.service-ANGvoV
drwx------ 3 root   root   4096 Dec  5 12:07 systemd-private-062a0eca7f2a44349733e78cb4abdff4-systemd-timesyncd.service-CdXUtH
-rw-rw-r-- 1 julien julien    0 Dec  5 12:09 unity_support_test.0
:) ^C
julien@ubuntu:~/shell$

Repo:

• GitHub repository: simple_shell

mandatory

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

Repo:

• GitHub repository: simple_shell

mandatory

Simple shell 0.4 +

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

julien@ubuntu:~/shell$ ./simple_shell
$ env
USER=julien
LANGUAGE=en_US
SESSION=ubuntu
COMPIZ_CONFIG_PROFILE=ubuntu
SHLVL=1
HOME=/home/julien
C_IS=Fun_:)
DESKTOP_SESSION=ubuntu
LOGNAME=julien
TERM=xterm-256color
PATH=/home/julien/bin:/home/julien/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
DISPLAY=:0
$ exit
julien@ubuntu:~/shell$

Repo:

• GitHub repository: simple_shell

mandatory

Write a blog post describing step by step what happens when you type ls -l *.c and hit Enter in a shell. Try to explain every step you know of, going in as much details as you can, give examples and draw diagrams when needed. You should merge your previous knowledge of the shell with the specifics of how it works under the hoods (including syscalls).

• Have at least one picture, at the top of the blog post
• Publish your blog post on Medium or LinkedIn
• Share your blog post at least on LinkedIn
• Only one blog post by team
• The blog post must be done and published before the first deadline (it will be part of the manual review)
• Please, remember that these blogs must be written in English to further your technical ability in a variety of settings