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?)
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
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)
Exmaple 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 cpmpiled 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
$
- Betty would be proud: Write a beautiful code that passes the Betty checks
- Simple shell 0.1: Write a UNIX command line interpreter. 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
execve will be the core part of your Shell, don’t forget to pass the environ to it…
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
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$
- Simple shell 0.2: Simple shell 0.1 + Handle command lines with arguments.
-
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$
- 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
-
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$
- 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
- Simple shell 0.2.1: Simple shell 0.2 +
You are not allowed to use strtok
- 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
- 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
- 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 $HOME
You have to handle the command cd -
You have to update the environment variable PWD when you change directory
man chdir, man getcwd
- ;: Simple shell 1.0 +
Handle the commands separator ;
alex@~$ 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@~$
- && 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@~$
- 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
- 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$
- Comments: Simple shell 1.0 +
Handle comments (#)
julien@ubuntu:~/shell$ sh
$ echo $$ # ls -la
5114
$ exit
julien@ubuntu:~/shell$
- 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
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