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https://github.com/samuelselasi/simple_shell

Custom Linux Shell
https://github.com/samuelselasi/simple_shell

bit-manipulation cprogramming-language execve file-input-output header-files linux-shell simple-shell strtok struct typedef

Last synced: 10 months ago
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Custom Linux Shell

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README 

          
# C Custom Linux Shell

## Background Context

* A simple UNIX command interpreter.

![shell](https://user-images.githubusercontent.com/85158665/219971433-f2b21b08-f3c0-491d-a13b-f925b05660f0.jpeg)

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

## Requirements

### General

* Editors: `vi`, `vim`

* All files compiled on Ubuntu 20.04 LTS using gcc, using the options `-Wall -Werror -Wextra -pedantic -std=gnu89`

* All files end with a new line

* Code uses the `Betty` style. Checked using [betty-style.pl](https://github.com/holbertonschool/Betty/blob/master/betty-style.pl) and [betty-doc.pl](https://github.com/holbertonschool/Betty/blob/master/betty-doc.pl)

* Shell has no memory leaks

* No more than 5 functions per file

* All header files are include guarded: [shell](./shell.h), [error](./error.h), [help](./help.h)

* System calls used only when needed ([why?](https://www.quora.com/Why-are-system-calls-expensive-in-operating-systems))

## More Info

### Output

* Custom shell has 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 is equivalent to the `argv[0]` (See below)

## Compilation

```

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

```

## Testing

Custom shell works 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. Code for custom shell complies with [Betty](https://medium.com/@onepunchcoder/writing-clean-effective-code-b29dcfb09ae) conventions.

```

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](./_getline.c)

	* Not implemented:

* Cursor movement

```

7. Simple shell 0.2.1

```

Simple shell 0.2 +

* Custom `strtok` function used

* [\_strtok](./_strtok.c)

```

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

1. Implement use of cursor

2. Implement use of symbols like `*`, `\` and ```

3. Display colours

4. Implement `tabs` for autocomplete

5. Implement more built-in functions

6. Improve `README.md` and `help` pages

7. Refactor code

## Authors

* Yasmine Ben Ali

* Selasi S. Kporvie