C Group project Syscall

Write a simple UNIX command interpreter.

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

Unix shell

Thompson shell

Ken Thompson

Everything you need to know to start coding your own shell

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”?

• A README.md file, at the root of the folder of the project with the description of your project
• Code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl
• Shell should not have any memory leaks
• No more than 5 functions per file
• Use system calls only when you need to (why?)
• You should have an AUTHORS file at the root of your repository

*There should be one project repository per group. Add your partner as a collaborator.

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
$

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

2. Simple shell 0.2

• Handle command lines with arguments

3. Simple shell 0.3

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

4. Simple shell 0.4

• 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

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

6. Simple shell 0.1.1

• Write your own getline function
• Use a buffer to read many chars at once and call the least possible the read system call
• You will need to use static variables
• You are not allowed to use getline

7. Simple shell 0.2.1

• You are not allowed to use strtok

8. Simple shell 0.4.1

• handle arguments for the built-in exit
• Usage: exit status, where status is an integer used to exit the shell

9. setenv, unsetenv

• Implement the setenv and unsetenv builtin commands

setenv

• Command syntax: setenv VARIABLE VALUE

unsetenv

• Command syntax: unsetenv VARIABLE

10. cd

• Implement the builtin command cd
• Command syntax: cd [DIRECTORY]
• If no argument is given to cd the command must be interpreted like cd $HOME

11. ;

• Handle the commands separator ;

12. && and ||

• Handle the && and || shell logical operators

13. alias

• Implement the alias builtin command
• Usage: alias [name[='value'] ...]

14. Variables

• Handle variables replacement
• Handle the $? variable
• Handle the $$ variable

15. Comments

• Handle comments (#)

16. File as input

• Usage: simple_shell [filename]

GitHub: Ononiwu Wisdom GitHub: Amure Samuel