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Simple Shell

Introduction

This repository is an Alx School Project. This project involves writing a shell like sh (Bourne Shell) by Stephen Bourne , in C, using a limited number of standard library functions, and practically applying we have learnt in C during the past 3 months Here

The goal in this project was to make us understand how a shell works. To single out some items: what is the environment, the difference between functions and system calls, how to create processes using execve...

Usage

In order to run this program,

Clone This Repo

git clone https://github.com/Slamchillz/simple_shell

compile it with

gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh.
You can then run it by invoking ./hsh in that same directory.

How to use it

In order to use this shell, in a terminal, first run the program:
prompt$ ./hsh
It wil then display a simple prompt and wait for commands.
($)
A command will be of the type $ command
This shell can handle two types of commands: builtins and normal program.

List of built-ins

Currently the list of built-ins I wrote is:

  • cd [directory]
    Switch to the specified directory (path).
  • env
    Displays the environment variable
  • exit [exitstatus]
    Exit from the program with exitstatus value. 0 by default.
  • setenv VARIABLE VALUE
    Sets the enviromental variable of key VARIABLE with the value of VALUE
  • unsetenv Unset an environment variable whose key is VARIABLE
  • echo [$$] or [$?] or [$PATH] Return pid and exit statue and PATH.
Command

Basicly Every Program in $PATH It Support Single Word like ls

It Support chaining commands like ls || ls && cp new.txt file.txt ; echo $OLDPWD

It Handle Path ls /tmp

it Handle Options Like ls -l

it Handle All Three Togther Like ls -l /var

it Handle Command Path Also Like /bin/ls And All The Option And Path Like /bin/ls -l /var

it Handle Comments #

Examples Command

Example 1

Username@your-regular-prompt:~$ ./hsh
($) pwd
/home/username/
($) ^D
Username@your-regular-prompt:~$

Example 2

Username@your-regular-prompt:~$ ./hsh
($) ls -l /tmp 
-rw------- 1 username username    0 Dec  5 12:09 config-err-aAMZrR
drwx------ 3 root   root   4096 Dec  5 12:09 systemd-private-062a0eca7f2a44349733e78cb4abdff4-colord.service-V7DUzr
drwx------ 3 root   root   4096 Dec  5 12:09 systemd-private-062a0eca7f2a44349733e78cb4abdff4-rtkit-daemon.service-ANGvoV
drwx------ 3 root   root   4096 Dec  5 12:07 systemd-private-062a0eca7f2a44349733e78cb4abdff4-systemd-timesyncd.service-CdXUtH
-rw-rw-r-- 1 username username    0 Dec  5 12:09 unity_support_test.0
($) ^D
Username@your-regular-prompt:~$

Exmples Builtin

case env and exit

Username@your-regular-prompt:~$ ./hsh
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
($) exit
Username@your-regular-prompt:~$

Case Exit Status

Username@your-regular-prompt:~$ ./hsh
($) exit 98
Username@your-regular-prompt:~$ echo $?
98
Username@your-regular-prompt:~$

Additional Features

  • Handle Ctrl+C: your shell should not quit when the user inputs ^C
  • If no argument is given to cd the command must be interpreted like cd $HOME
  • handle the command cd -
  • Handle variables replacement
  • Handle the $? variable
  • Handle the $$ variable
  • Handle batch mode like ./hsh [filename] Where test is a file filled with command and builtin to excute.

List of functions and system calls we could use

List of allowed 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)
fork (man 2 fork)
free (man 3 free)
fstat (man 2 fstat)
getcwd (man 3 getcwd)
getline (man 3 getline)
kill (man 2 kill)
lstat (man 2 lstat)
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 (man 2 stat)
strtok (man 3 strtok)
wait (man 2 wait)
waitpid (man 2 waitpid)
wait3 (man 2 wait3)
wait4 (man 2 wait4)
write (man 2 write)
_exit (man 2 _exit)

Custom Function (Recreation of Standard Function in C)

  • _strncpy
  • _strlen
  • _putchar
  • _atoi
  • _puts
  • _strcmp
  • _isalpha
  • _reverse
  • intlen
  • _itoa
  • _join
  • _strcpy
  • _strchr
  • _strncmp
  • _strdup
  • _realloc
  • _freearray
  • _getenv
  • _readline
  • _tokenise
  • _hashtag

For More Info About It Check The Man Page by

Username@your-regular-prompt:~$ man ./man_1_simple_shell

Project Done in 15 Days

Author