newbie.c - A Simple Custom Shell Implementation

Purpose

This project implements a basic command-line shell for educational purposes. It demonstrates core concepts in C programming, including:

• Standard input/output handling
• Dynamic memory allocation (malloc, realloc)
• String manipulation
• Process creation and management (fork, execvp, wait)

Features

• Customizable Prompt: Displays the username as part of the shell prompt.
• Command Execution: Executes system commands entered by the user.
• Graceful Exit: Handles 'quit' and 'exit' commands to terminate the shell.

How to Use

1. Compile the code:

   gcc newbie.c -o newbie 

2. Run the executable:

   ./newbie 

Example Interaction

newbie@linuxuser >$ ls -a
.    ..   newbie  newbie.c  README.md
newbie@linuxuser >$ date
Sun Apr 14 09:56:10 IST 2024
newbie@linuxuser >$ exit
Thank You for Using newbie shell

Understanding the Code

• Header Files: Includes necessary standard libraries.
• Global Variables: Defines variables storing input state and username.
• readinput() function:
  • Reads user input character by character until a space or newline is encountered.
  • Dynamically allocates memory for the input string.
• runcommand() function:
  • Creates a child process using fork().
  • Executes the specified command using execvp().
  • Waits for child process termination using wait().
• main() function:
  • Retrieves the username from the USER environment variable.
  • Implements the main shell loop:
    • Displays the prompt.
    • Reads command input using readinput().
    • Parses input into commands and arguments.
    • Executes commands (or handles 'quit' / 'exit').

Notes

• This is a simplified shell implementation and lacks features like command history, I/O redirection, and advanced argument parsing.
• Consider exploring these enhancements for additional learning.