Project Name

0x16. C - Simple Shell

Table of Contents

• Project Description
• Requirements
• Authorized functions and macros
• Compilation
• Tasks
• Known Bugs
• Collaborate

Project Description

Simple_shell is a command line interpreter, or shell, in the tradition of the first Unix shell written by Ken Thompson in 1971. This shell is intentionally minimalistic, yet includes the basic functionality of a traditional Unix-like command line user interface.

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.
• Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl.
• All your files should end with a new line.
• You are not allowed to use global variables.
• No more than 5 functions per file.
• All your header files should be include guarded.
• You should have an AUTHORS file at the root of your repository, listing all individuals having contributed content to the repository. Format, see Docker.

Authorized 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)

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
$

Compilation

Your code 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
$

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.

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

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$

---

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.

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$ 

---

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.

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$ 

---

6. Simple shell 0.1.1

Simple shell 0.1 +

• 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.

You don’t have to:

• Be able to move the cursor.

---

7. Simple shell 0.2.1

Simple shell 0.2 +

• You are not allowed to use strtok.

---

8. Simple shell 0.4.1

Simple shell 0.4 +

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

julien@ubuntu:~/shell$ ./shell_0.4.1
$ exit 98
julien@ubuntu:~/shell$ echo $?
98
julien@ubuntu:~/shell$ 

---

9. setenv, unsetenv

Simple shell 1.0 +

Implement the setenv and unsetenv builtin commands:

• setenv
  • Initialize a new environment variable, or modify an existing one.
  • Command syntax: setenv VARIABLE VALUE.
  • Should print something on stderr on failure.
• unsetenv
  • Remove an environment variable.
  • Command syntax: unsetenv VARIABLE.
  • Should print something on stderr on failure.

---

10. cd

Simple shell 1.0 +

Implement the builtin command cd:

• Changes the current directory of the process.
• Command syntax: cd [DIRECTORY].
• If no argument is given to cd the command must be interpreted like cd $HOME.
• You have to handle the command cd -.
• You have to update the environment variable PWD when you change directory.

man chdir, man getcwd

---

11. ;

Simple shell 1.0 +

• Handle the commands separator ;.

alex@~$ ls /var ; ls /var
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
alex@~$ ls /hbtn ; ls /var
ls: cannot access /hbtn: No such file or directory
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
alex@~$ ls /var ; ls /hbtn
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
ls: cannot access /hbtn: No such file or directory
alex@~$ ls /var ; ls /hbtn ; ls /var ; ls /var
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
ls: cannot access /hbtn: No such file or directory
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
alex@~$

---

12. && and ||

Simple shell 1.0 +

• Handle the && and || shell logical operators.

alex@~$ ls /var && ls /var
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
alex@~$ ls /hbtn && ls /var
ls: cannot access /hbtn: No such file or directory
alex@~$ ls /var && ls /var && ls /var && ls /hbtn
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
ls: cannot access /hbtn: No such file or directory
alex@~$ ls /var && ls /var && ls /var && ls /hbtn && ls /hbtn
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
ls: cannot access /hbtn: No such file or directory
alex@~$
alex@~$ ls /var || ls /var
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
alex@~$ ls /hbtn || ls /var
ls: cannot access /hbtn: No such file or directory
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
alex@~$ ls /hbtn || ls /hbtn || ls /hbtn || ls /var
ls: cannot access /hbtn: No such file or directory
ls: cannot access /hbtn: No such file or directory
ls: cannot access /hbtn: No such file or directory
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
alex@~$ ls /hbtn || ls /hbtn || ls /hbtn || ls /var || ls /var
ls: cannot access /hbtn: No such file or directory
ls: cannot access /hbtn: No such file or directory
ls: cannot access /hbtn: No such file or directory
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  spool  tmp
alex@~$

---

13. alias

Simple shell 1.0 +

• Implement the alias builtin command.
• Usage: alias [name[='value'] ...]:
  • alias: Prints a list of all aliases, one per line, in the form * name='value'.
  • alias name [name2 ...]: Prints the aliases name, name2, etc 1 per line, in the form name='value'.
  • alias name='value' [...]: Defines an alias for each name whose value is given. If name is already an alias, replaces its value with value.

---

14. Variables

Simple shell 1.0 +

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

julien@ubuntu:~/shell$ ./hsh
$ ls /var
backups  cache  crash  lib  local  lock  log  mail  metrics  opt  run  snap  spool  tmp
$ echo $?
0
$ echo $$
5104
$ echo $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
$ exit 
julien@ubuntu:~/shell$ 

---

15. Comments

Simple shell 1.0 +

• Handle comments (#)

julien@ubuntu:~/shell$ sh
$ echo $$ # ls -la
5114
$ exit
julien@ubuntu:~/shell$ 

---

16. File as input

Simple shell 1.0 +

• Usage: simple_shell [filename].
• Your shell can take a file as a command line argument.
• The file contains all the commands that your shell should run before exiting.
• The file should contain one command per line.
• In this mode, the shell should not print a prompt and should not read from stdin.

---

Known Bugs

There are a number of bugs starting from task 0.

Collaborate

To collaborate, reach us through the email addresses in the AUTHORS file.