Simple Shell 🔥

---

Description

This repository contains the files to simulate a basic Unix Shell with its respective commands. It uses the POSIX API to implement many of the same functionalities of the first Ken Thompson's Shell.

In C language, header files (.h) contain a set of predefined standard library functions. The .h is the extension of the header files in C and we request to use a header file in our program by including it with the C preprocessing directive #include <file_name.h>. C language has numerous libraries that include predefined functions to make programming easier. The predominantly used system and function calls used in this program are read, write, open, execve, exit, fflush, fork, free, malloc, getline, isatty, perror, strtok, wait, and waitpid.

This simple shell is a Shell interface written in the C programming language that gives to the user a prompt $ and executes a user-inputted command. The shell is used directly to interact with the Kernel that hosts the OS.

Main Features

• This program displays a prompt and waits for the user to type a command. A command line always ends with a new line (when the user pushes the ENTER key).
• The prompt is displayed again each time a command has been executed.
• When the user enters exit, the shell will end and returns the status 0.
• The user could stop the program using Ctrl+D (end of file).
• The shell handles the command lines with arguments and pathways.
• The program does not quit when the user inputs ^C (Ctrl+C).
• This program executes the most common shell commands as ls, grep, find, pwd, rm, cp, mv, exit, etc... with arguments.
• If an executable cannot be found, it prints an error message and displays the prompt again.
• This Shell does not support commentaries using #.
• This shell does not support pipes |, shell logical operators such as && or ||, neither commands separator ;.

Requirements

• Operating System: Ubuntu 14.04 LTS

• Compiler: GCC 4.8.4

Program Execution Workflow

The next steps are a brief description of how the shell works:

1. First, the parent process is created when the user runs the program.
2. Then, the isatty() function using the STDIN_FILENO file descriptor -fd- tests if there is an open file descriptor referring to a terminal. If isatty() returns 1, the prompt is shown using write() with STDOUT_FILENO as fd and waits for input from the user on the command line.
3. When the user types a command, the getline() function reads an entire line from the input stream, and strtok() function breaks the inputted command into a sequence of non-empty tokens.
4. Next, it creates a separate child process using fork() that performs the inputted command. Unless otherwise specified, the parent process waits for the child to exit before continuing.
5. After tokenizing the command, execve() executes it, and all allocated memory is freed using free().
6. Finally, the program returns to main(), prints the prompt, and waits for another user input.

Implementation

To run this shell with its respective commands, clone this repository in your terminal.

• HTTPS:

git clone https://github.com/richie-omondi/simple_shell.git

• SSH:

git clone [email protected]:richie-omondi/simple_shell.git

Compilation

gcc -Wall -Wextra -Werror -pedantic -ggdb3 *.c -o hsh

Debugging

• If you want to debug the shell, use valgrind:

valgrind --track-origins=yes --leak-check=full --show-leak-kinds=all -s ./hsh

More info on Valgrind can be found here: https://valgrind.org/

• Or just run and try this shell using:

./hsh

Examples

Here are shown some examples of the usage of the Shell:

• ls

($) ls
add_shell_data.c  debugging.txt  errors.c         free.c  memory_functions.c  print.c    shell.c  string_functions_2.c  Tasks.md   tokenize.c
AUTHORS           env.c          execute_shell.c  hsh     Notes.md            README.md  shell.h  string_functions.c    test_ls_2

($) /bin/ls
add_shell_data.c  debugging.txt  errors.c         free.c  memory_functions.c  print.c    shell.c  string_functions_2.c  Tasks.md   tokenize.c
AUTHORS           env.c          execute_shell.c  hsh     Notes.md            README.md  shell.h  string_functions.c    test_ls_2

($) ls -lat
total 108
-rwxr-xr-x 1 root root 23184 Aug 20 07:06 hsh
drwxr-xr-x 3 root root  4096 Aug 20 07:06 .
drwxr-xr-x 8 root root   220 Aug 20 07:06 .git
-rw-r--r-- 1 root root  3957 Aug 20 07:06 README.md
-rw-r--r-- 1 root root  2051 Aug 13 14:20 shell.h
-rw-r--r-- 1 root root  2727 Aug 13 14:20 shell.c
-rw-r--r-- 1 root root  1252 Aug 13 14:16 free.c
-rw-r--r-- 1 root root  2955 Aug 13 07:45 tokenize.c
drwxr-xr-x 1 root root   170 Aug 12 13:49 ..
-rw-r--r-- 1 root root  1667 Aug  9 06:20 string_functions_2.c
-rw-r--r-- 1 root root    16 Aug  9 06:20 test_ls_2
-rw-r--r-- 1 root root   773 Aug  9 06:20 add_shell_data.c
-rw-r--r-- 1 root root    81 Aug  9 06:20 AUTHORS
-rw-r--r-- 1 root root    79 Aug  9 06:20 debugging.txt
-rw-r--r-- 1 root root   957 Aug  9 06:20 env.c
-rw-r--r-- 1 root root   951 Aug  9 06:20 errors.c
-rw-r--r-- 1 root root   862 Aug  9 06:20 execute_shell.c
-rw-r--r-- 1 root root   636 Aug  9 06:20 memory_functions.c
-rw-r--r-- 1 root root  8624 Aug  9 06:20 Notes.md
-rw-r--r-- 1 root root   272 Aug  9 06:20 print.c
-rw-r--r-- 1 root root  2224 Aug  9 06:20 string_functions.c
-rw-r--r-- 1 root root  1574 Aug  9 06:20 Tasks.md

• pwd

($) pwd
/simple_shell

• echo

($) echo Hello World
Hello World

• Ctrl+D and Ctrl+C

($) ^C
($)
vagrant@vagrant-ubuntu-trusty-64:~/ALX/simple_shell$ 

Note that in the second line the Ctrl+D is typed

Authors:

• Richard Orido - @richie-omondi
• Maxmillan Rutto - @Maxrutto