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0x16. C - Simple Shell

Introduction

This repository is a ALX Project. The school project consisted in writing a shell like sh (Bourne Shell) by Stephen Bourne , in C, using a limited number of standard library functions, So Instead we used ower own function that we rewrited over the past three month 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/youssefelzedy/simple_shell

compile it with

gcc 4.8.4 -Wall -Werror -Wextra -pedantic *.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]
    note: not complate 100%
    Switch to the specified directory (path).
  • env
    Displays the environment variable
  • exit [exitstatus]
    Exit from the program with exitstatus value. 0 by default.
Command

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

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 Statue

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

Keep Exploring The echo Builtin and history ... Using The Help Builtin

Also

  • 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

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)
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)
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
  • _nan
  • _itoa
  • _strcat
  • _strcpy
  • _strchr
  • _strncmp
  • _strdup
  • _getenv
  • _getline
  • _strtok

Project Done in 15 Day

Authors