0x16. C - Simple Shell

Authors

Mojalefa Kodisang & Habiba Zguaid

Description

The project was focused more on building a simple shell with similar capabilities as the sh builtin shell.

Our should handle every case that are handle by sh as we are going to explain in detail in this document. Here are the concepts required to build the project:

Basics of C programming

Basic shell / bash commands

How does our prompt work?

Compilation

For compilation we used gcc compiler, which compiles all .c files and using the following flags as seen below :

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

Execution

To run the program, you need to execute the program name hsh on to your bash prompt. Upon execution a prompt woulf appear, see example below:

julien@ubuntu:~/shell$ ./hsh
:)  

Handles

Our prompt handles a limited cases. Here are some of the cases it handles:

1. UNIX command line interpretion

julien@ubuntu:~/shell$ ./hsh
:)
:) Ctrl+D
julien@ubuntu:~/shell$

2. Handle command lines with arguments

julien@ubuntu:~/shell$
:) /bin/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$

3. Handle the PATH
   • fork must not be called if the command doesn’t exist

   Warning: This case has a memory leakage problem of which we are going to fix soon

julien@ubuntu:~/shell$ ./hsh
:) /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$

4. Implement the exit built-in, that exits the shell without arguments

julien@ubuntu:~/shell$ ./hsh
:) exit
julien@ubuntu:~/shell$

5. env built-in, that prints the current environment

julien@ubuntu:~/shell$ ./hsh
:) 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$

6. builtin command cd

julien@ubuntu:~/shell$ ./hsh
:) cd [directory]
:)
:) exit
julien@ubuntu:~/shell$

How to get this get this project?

$ git clone https://github.com/zguaidh/simple_shell

copyrights reserved 2023
ALX - African Leadership International
M. Kodisang and B. Zguaid