0x16. C - Simple Shell

Background Context

A simple UNIX command interpreter. ^ “The Gates of Shell”, by Spencer Cheng, featuring Julien Barbier

Learning Objectives

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

General

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”?

Requirements`

General

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

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)

Compilation

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

Testing

Your shell should work like this in interactive mode:

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ /bin/ls
AUTHORS    _getline.c  _strcmp.c   _strcpy.c  _strtok.c  built_in.c  error.c    expansions.c  help.h     input.c        memory_func2.c  pow_b.c  shell.h     test_ls_2
README.md  _itoa.c     _strcmpd.c  _strdup.c  _write.c   cd.c        error.h    file_path.c   history.c  linked_lists.c  num_len.c                                                                                                           run.c     sometest    unalias.c
_atoi.c    _strcat.c   _strcmps.c  _strlen.c  alias.c    env_func.c  execute.c  help.c        hsh        memory_func1.c  parser.c                                                                                                            shell.c  str_func.c
$ exit
vagrant@ubuntu-focal:~/simple_shell$

And also in non-interactive mode:

vagrant@ubuntu-focal:~/simple_shell$ echo "/bin/ls" | ./hsh
AUTHORS    _getline.c  _strcmp.c   _strcpy.c  _strtok.c  built_in.c  error.c    expansions.c  help.h     input.c        memory_func2.c  pow_b.c  shell.h     test_ls_2
README.md  _itoa.c     _strcmpd.c  _strdup.c  _write.c   cd.c        error.h    file_path.c   history.c  linked_lists.c  num_len.c                                                                                                           run.c     sometest    unalias.c
_atoi.c    _strcat.c   _strcmps.c  _strlen.c  alias.c    env_func.c  execute.c  help.c        hsh        memory_func1.c  parser.c                                                                                                            shell.c  str_func.c
vagrant@ubuntu-focal:~/simple_shell$

Tasks

0. Betty would be proud

Code passes Betty checks.

Run betty * to verify

1. Simple shell 0.1

UNIX command line interpreter
Usage: simple_shell
The shell:
Displays a prompt and waits for the user to type a command.
The prompt is displayed again each time a command has been executed.
The command line always ends with a new line.
If an executable cannot be found, prints an error message and displays the prompt again.
Handles the “end of file” condition (Ctrl+D) gif here:

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

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ /bin/ls
AUTHORS    _getline.c  _strcmp.c   _strcpy.c  _strtok.c  built_in.c  error.c    expansions.c  help.h     input.c        memory_func2.c  pow_b.c  shell.h     test_ls_2
README.md  _itoa.c     _strcmpd.c  _strdup.c  _write.c   cd.c        error.h    file_path.c   history.c  linked_lists.c  num_len.c                                                                                                           run.c     sometest    unalias.c
_atoi.c    _strcat.c   _strcmps.c  _strlen.c  alias.c    env_func.c  execute.c  help.c        hsh        memory_func1.c  parser.c                                                                                                            shell.c  str_func.c
$ ls
AUTHORS    _getline.c  _strcmp.c   _strcpy.c  _strtok.c  built_in.c  error.c    expansions.c  help.h     input.c        memory_func2.c  pow_b.c  shell.h     test_ls_2
README.md  _itoa.c     _strcmpd.c  _strdup.c  _write.c   cd.c        error.h    file_path.c   history.c  linked_lists.c  num_len.c                                                                                                           run.c     sometest    unalias.c
_atoi.c    _strcat.c   _strcmps.c  _strlen.c  alias.c    env_func.c  execute.c  help.c        hsh        memory_func1.c  parser.c                                                                                                            shell.c  str_func.c
$ ls -l /tmp
total 20
drwx------ 3 root root 4096 Feb 21 06:57 snap-private-tmp
drwx------ 3 root root 4096 Feb 21 06:57 systemd-private-66e4732a88ba4d62b85b74050f0d0ead-ModemManager.service-8vrZtj
drwx------ 3 root root 4096 Feb 21 06:57 systemd-private-66e4732a88ba4d62b85b74050f0d0ead-systemd-logind.service-09pvYi
drwx------ 3 root root 4096 Feb 21 06:57 systemd-private-66e4732a88ba4d62b85b74050f0d0ead-systemd-resolved.service-iInQXh
drwx------ 3 root root 4096 Feb 21 06:57 systemd-private-66e4732a88ba4d62b85b74050f0d0ead-systemd-timesyncd.service-a6bQAf
$ ^C
$
vagrant@ubuntu-focal:~/simple_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

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ exit
vagrant@ubuntu-focal:~/simple_shell$

5. Simple shell 1.0

Simple shell 0.4 +

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

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ env
SHELL=/bin/bash
PWD=/home/vagrant/simple_shell
LOGNAME=vagrant
XDG_SESSION_TYPE=tty
MOTD_SHOWN=pam
HOME=/home/vagrant
LANG=C.UTF-8
LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.zst=01;31:*.tzst=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.wim=01;31:*.swm=01;31:*.dwm=01;31:*.esd=01;31:*.jpg=01;35:*.jpeg=01;35:*.mjpg=01;35:*.mjpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36:
SSH_CONNECTION=10.0.2.2 56291 10.0.2.15 22
LESSCLOSE=/usr/bin/lesspipe %s %s
XDG_SESSION_CLASS=user
TERM=xterm-256color
LESSOPEN=| /usr/bin/lesspipe %s
USER=vagrant
SHLVL=1
XDG_SESSION_ID=12
XDG_RUNTIME_DIR=/run/user/1000
SSH_CLIENT=10.0.2.2 56291 22
XDG_DATA_DIRS=/usr/local/share:/usr/share:/var/lib/snapd/desktop
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
SSH_TTY=/dev/pts/0
OLDPWD=/home/vagrant
_=./hsh
$

6. Simple shell 0.1.1

Simple shell 0.1 +

Custom getline function
Use a buffer to read many chars at once and call the least possible the read system call
Use of static variables
Global getline function not used
_getline
- Not implemented:
Cursor movement

7. Simple shell 0.2.1

Simple shell 0.2 +

Custom strtok function used
_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

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ exit 98
vagrant@ubuntu-focal:~/simple_shell$ echo $?
98
vagrant@ubuntu-focal:~/simple_shell$

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

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ setenv SOME_VAR 13
$ echo $SOME_VAR
13
$ unsetenv SOME_VAR
$ echo $SOME_VAR

$

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
- Handles the command cd -
- Environment variable PWD is updated when you change directory

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ pwd
/home/vagrant/simple_shell
$ cd
$ pwd
/home/vagrant
$ cd -
$ pwd
/home/vagrant/simple_shell
$

11. ;

Simple shell 1.0 +

Handles the commands separator ;

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ ls /var ; ls /var
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
$ ls /hbtn ; ls /var
ls: cannot access '/hbtn': No such file or directory
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
$ ls /var ; ls /hbtn
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
ls: cannot access '/hbtn': No such file or directory
$ ls /var ; ls /hbtn ; ls /var ; ls /var
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
ls: cannot access '/hbtn': No such file or directory
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
$

12. && and ||

Simple shell 1.0 +

Handle the && and || shell logical operators

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ ls /var && ls /var
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
$ ls /hbtn && ls /var
ls: cannot access '/hbtn': No such file or directory
$ ls /var && ls /var && ls /var && ls /hbtn
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
ls: cannot access '/hbtn': No such file or directory
$ ls /var && ls /var && ls /var && ls /hbtn && ls /hbtn
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
ls: cannot access '/hbtn': No such file or directory
$
$ ls /var || ls /var
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
$ ls /hbtn || ls /var
ls: cannot access '/hbtn': No such file or directory
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
$ 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  opt  run  snap  spool  tmp
$ 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  opt  run  snap  spool  tmp
$

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

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ alias lister='ls -l'
$ alias pathfinder="pwd"
$ alias shouter=echo
$ alias
lister='ls -l'
pathfinder='pwd'
shouter='echo'
$ alias shouter
shouter='echo'
$ alias pathfinder
pathfinder='pwd'
$ lister
total 204
-rw-rw-r-- 1 vagrant vagrant   136 Feb 21 18:00 AUTHORS
-rw-rw-r-- 1 vagrant vagrant  4021 Feb 21 18:00 README.md
-rw-rw-r-- 1 vagrant vagrant   397 Feb 21 18:00 _atoi.c
-rw-rw-r-- 1 vagrant vagrant  1041 Feb 21 18:00 _getline.c
-rw-rw-r-- 1 vagrant vagrant   835 Feb 21 18:00 _itoa.c
-rw-rw-r-- 1 vagrant vagrant   290 Feb 21 18:00 _strcat.c
-rw-rw-r-- 1 vagrant vagrant   356 Feb 21 18:00 _strcmp.c
-rw-rw-r-- 1 vagrant vagrant   391 Feb 21 18:00 _strcmpd.c
-rw-rw-r-- 1 vagrant vagrant   421 Feb 21 18:00 _strcmps.c
-rw-rw-r-- 1 vagrant vagrant   280 Feb 21 18:00 _strcpy.c
-rw-rw-r-- 1 vagrant vagrant   357 Feb 21 18:00 _strdup.c
-rw-rw-r-- 1 vagrant vagrant   267 Feb 21 18:00 _strlen.c
-rw-rw-r-- 1 vagrant vagrant  1205 Feb 21 18:00 _strtok.c
-rw-rw-r-- 1 vagrant vagrant   819 Feb 21 18:00 _write.c
-rw-rw-r-- 1 vagrant vagrant  3028 Feb 21 18:00 alias.c
-rw-rw-r-- 1 vagrant vagrant  2355 Feb 21 18:00 built_in.c
-rw-rw-r-- 1 vagrant vagrant   901 Feb 21 18:00 cd.c
-rw-rw-r-- 1 vagrant vagrant  2982 Feb 21 18:00 env_func.c
-rw-rw-r-- 1 vagrant vagrant   707 Feb 21 18:00 error.c
-rw-rw-r-- 1 vagrant vagrant   915 Feb 21 18:00 error.h
-rw-rw-r-- 1 vagrant vagrant   539 Feb 21 18:00 execute.c
-rw-rw-r-- 1 vagrant vagrant  2039 Feb 21 18:00 expansions.c
-rw-rw-r-- 1 vagrant vagrant   829 Feb 21 18:00 file_path.c
-rw-rw-r-- 1 vagrant vagrant  1067 Feb 21 18:00 help.c
-rw-rw-r-- 1 vagrant vagrant  2814 Feb 21 18:00 help.h
-rw-rw-r-- 1 vagrant vagrant  1697 Feb 21 18:00 history.c
-rwxrwxr-x 1 vagrant vagrant 41760 Feb 21 18:00 hsh
-rw-rw-r-- 1 vagrant vagrant   557 Feb 21 18:00 input.c
-rw-rw-r-- 1 vagrant vagrant  3240 Feb 21 18:00 linked_lists.c
-rw-rw-r-- 1 vagrant vagrant  2121 Feb 21 18:00 memory_func1.c
-rw-rw-r-- 1 vagrant vagrant   334 Feb 21 18:00 memory_func2.c
-rw-rw-r-- 1 vagrant vagrant   268 Feb 21 18:00 num_len.c
-rw-rw-r-- 1 vagrant vagrant  1143 Feb 21 18:00 parser.c
-rw-rw-r-- 1 vagrant vagrant   272 Feb 21 18:00 pow_b.c
-rw-rw-r-- 1 vagrant vagrant  1081 Feb 21 18:00 run.c
-rw-rw-r-- 1 vagrant vagrant  3723 Feb 21 18:00 shell.c
-rw-rw-r-- 1 vagrant vagrant  2575 Feb 21 18:00 shell.h
-rw-rw-r-- 1 vagrant vagrant    74 Feb 21 18:00 sometest
-rw-rw-r-- 1 vagrant vagrant  1267 Feb 21 18:00 str_func.c
-rw-rw-r-- 1 vagrant vagrant    10 Feb 21 18:00 test_ls_2
-rw-rw-r-- 1 vagrant vagrant   672 Feb 21 18:00 unalias.c
$ shouter $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
$ pathfinder
/home/vagrant/simple_shell
$

14. Variables

Simple shell 1.0 +

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

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ ls /var
backups  cache  crash  lib  local  lock  log  mail  opt  run  snap  spool  tmp
$ echo $?
0
$ echo $$
25100
$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
$ exit
vagrant@ubuntu-focal:~/simple_shell$

15. Comments

Simple shell 1.0 +

Handle comments (#)

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ echo $$ # ls -la
25146
$ exit
vagrant@ubuntu-focal:~/simple_shell$

16. File as input

Simple shell 1.0 +

Usage: simple_shell [filename]
The 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

vagrant@ubuntu-focal:~/simple_shell$ cat test_ls_2
ls
pwd
ls
vagrant@ubuntu-focal:~/simple_shell$ ./hsh test_ls_2
AUTHORS    _getline.c  _strcmp.c   _strcpy.c  _strtok.c  built_in.c  error.c    expansions.c  help.h     input.c        memory_func2.c  pow_b.c  shell.h     test_ls_2
README.md  _itoa.c     _strcmpd.c  _strdup.c  _write.c   cd.c        error.h    file_path.c   history.c  linked_lists.c  num_len.c                                                                                                           run.c     sometest    unalias.c
_atoi.c    _strcat.c   _strcmps.c  _strlen.c  alias.c    env_func.c  execute.c  help.c        hsh        memory_func1.c  parser.c                                                                                                            shell.c  str_func.c
/home/vagrant/simple_shell
AUTHORS    _getline.c  _strcmp.c   _strcpy.c  _strtok.c  built_in.c  error.c    expansions.c  help.h     input.c        memory_func2.c  pow_b.c  shell.h     test_ls_2
README.md  _itoa.c     _strcmpd.c  _strdup.c  _write.c   cd.c        error.h    file_path.c   history.c  linked_lists.c  num_len.c                                                                                                           run.c     sometest    unalias.c
_atoi.c    _strcat.c   _strcmps.c  _strlen.c  alias.c    env_func.c  execute.c  help.c        hsh        memory_func1.c  parser.c                                                                                                            shell.c  str_func.c
vagrant@ubuntu-focal:~/simple_shell$

Error Messages

Handles errors when commands fail and prints error message to stderr

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ nonexistent
./hsh: 1: nonexistent: not found
$ cd nodirectory
./hsh: 2: cd: nodirectory: No such file or directory
$ alias notset
./hsh: 3: alias: notset: not found
$ setenv noneset
./hsh: 4: setenv: Syntax error
$ unsetenv none
$ exit notint
./hsh: 6: exit: notint: numeric argument required
vagrant@ubuntu-focal:~/simple_shellu$

Help

Enter help in shell to get more info on built-in functions

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ help

Simple Shell    Version 1-ALX Software Engineering Team Project(Yasmine B. Ali & Selasi S. Kporvie)
These shell commands are defined in the custom shell.
Type `help' to see this list.
Type `help name' to find out more about the function `name'.

The following commands are defined:

        alias [name[='value'] ...]      help
        cd [DIRECTORY]                  history
        env                             setenv [VARIABLE] [VALUE]
        exit [status]                   unsetenv [VARIABLE]
$ help alias
        alias usage: alias [name[='value'] ...]
        alias: Prints a list of all aliases, one per line, in the form 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
        or overwrites the KEY with new VALUE.
$ help cd
        cd usage: cd [DIRECTORY]
        If no argument is given to cd the command must be interpreted like cd $HOME
        cd - changes directory to the precious directory
        the environment variable PWD is updated when cd is used
$ help env
        env usage: env
        Prints out the current envirornment variables.
$ help exit
        exit usage: exit status
        Exits the shell with or without an integer status
        Last command executed before shell terminates
$ help history
        history usage: history
        Displays history of commands in shell
$ help help
        help usage: help COMMAND
        Displays helpful info about builtins
$ help setenv
        setenv usage: setenv VARIABLE VALUE
        Initialize a new environment variable, or modify an existing one
        Prints syntax error on stderr on failure
$ help unsetenv
        unsetenv usage: unsetenv VARIABLE
        Remove an environment variable
        Prints syntax error on sterr on failure
$

Bugs

Unable to print alias in the form alias lister if lister is an alias with a flag like 'ls -l'. WOrks fine if alias is not a flag.

vagrant@ubuntu-focal:~/simple_shell$ ./hsh
$ alias lister='ls -l'
$ lister
total 204
-rw-rw-r-- 1 vagrant vagrant   136 Feb 21 18:00 AUTHORS
-rw-rw-r-- 1 vagrant vagrant  4021 Feb 21 18:00 README.md
-rw-rw-r-- 1 vagrant vagrant   397 Feb 21 18:00 _atoi.c
-rw-rw-r-- 1 vagrant vagrant  1041 Feb 21 18:00 _getline.c
-rw-rw-r-- 1 vagrant vagrant   835 Feb 21 18:00 _itoa.c
-rw-rw-r-- 1 vagrant vagrant   290 Feb 21 18:00 _strcat.c
-rw-rw-r-- 1 vagrant vagrant   356 Feb 21 18:00 _strcmp.c
-rw-rw-r-- 1 vagrant vagrant   391 Feb 21 18:00 _strcmpd.c
-rw-rw-r-- 1 vagrant vagrant   421 Feb 21 18:00 _strcmps.c
-rw-rw-r-- 1 vagrant vagrant   280 Feb 21 18:00 _strcpy.c
-rw-rw-r-- 1 vagrant vagrant   357 Feb 21 18:00 _strdup.c
-rw-rw-r-- 1 vagrant vagrant   267 Feb 21 18:00 _strlen.c
-rw-rw-r-- 1 vagrant vagrant  1205 Feb 21 18:00 _strtok.c
-rw-rw-r-- 1 vagrant vagrant   819 Feb 21 18:00 _write.c
-rw-rw-r-- 1 vagrant vagrant  3028 Feb 21 18:00 alias.c
-rw-rw-r-- 1 vagrant vagrant  2355 Feb 21 18:00 built_in.c
-rw-rw-r-- 1 vagrant vagrant   901 Feb 21 18:00 cd.c
-rw-rw-r-- 1 vagrant vagrant  2982 Feb 21 18:00 env_func.c
-rw-rw-r-- 1 vagrant vagrant   707 Feb 21 18:00 error.c
-rw-rw-r-- 1 vagrant vagrant   915 Feb 21 18:00 error.h
-rw-rw-r-- 1 vagrant vagrant   539 Feb 21 18:00 execute.c
-rw-rw-r-- 1 vagrant vagrant  2039 Feb 21 18:00 expansions.c
-rw-rw-r-- 1 vagrant vagrant   829 Feb 21 18:00 file_path.c
-rw-rw-r-- 1 vagrant vagrant  1067 Feb 21 18:00 help.c
-rw-rw-r-- 1 vagrant vagrant  2814 Feb 21 18:00 help.h
-rw-rw-r-- 1 vagrant vagrant  1697 Feb 21 18:00 history.c
-rwxrwxr-x 1 vagrant vagrant 41760 Feb 21 18:00 hsh
-rw-rw-r-- 1 vagrant vagrant   557 Feb 21 18:00 input.c
-rw-rw-r-- 1 vagrant vagrant  3240 Feb 21 18:00 linked_lists.c
-rw-rw-r-- 1 vagrant vagrant  2121 Feb 21 18:00 memory_func1.c
-rw-rw-r-- 1 vagrant vagrant   334 Feb 21 18:00 memory_func2.c
-rw-rw-r-- 1 vagrant vagrant   268 Feb 21 18:00 num_len.c
-rw-rw-r-- 1 vagrant vagrant  1143 Feb 21 18:00 parser.c
-rw-rw-r-- 1 vagrant vagrant   272 Feb 21 18:00 pow_b.c
-rw-rw-r-- 1 vagrant vagrant  1081 Feb 21 18:00 run.c
-rw-rw-r-- 1 vagrant vagrant  3723 Feb 21 18:00 shell.c
-rw-rw-r-- 1 vagrant vagrant  2575 Feb 21 18:00 shell.h
-rw-rw-r-- 1 vagrant vagrant    74 Feb 21 18:00 sometest
-rw-rw-r-- 1 vagrant vagrant  1267 Feb 21 18:00 str_func.c
-rw-rw-r-- 1 vagrant vagrant    10 Feb 21 18:38 test_ls_2
-rw-rw-r-- 1 vagrant vagrant   672 Feb 21 18:00 unalias.c
$ alias
lister='ls -l'
$ alias lister
./hsh: 4: alias: ls: not found
./hsh: 4: alias: -l: not found
$

Future Tasks

Implement use of cursor
Implement use of symbols like *, \ and ```
Display colours
Implement tabs for autocomplete
Implement more built-in functions
Improve README.md and help pages
Refactor code

Authors

Yasmine Ben Ali
Selasi S. Kporvie

NewGit1999/simple_shell

0x16. C - Simple Shell

Background Context

Learning Objectives

General

Requirements`

General

More Info

Output

Compilation

Testing

Tasks

Error Messages

Help

Bugs

Future Tasks

Authors