vsh - Shell Implementation

Overview

vsh is a simple command-line shell implemented in C. It reads user commands, parses them into arguments, and executes them. The shell supports built-in commands (cd, help, exit) and can also execute external programs using the execvp system call.

Features

• Supports built-in commands:
  • cd <directory>: Change directory
  • help: Display available built-in commands
  • exit: Exit the shell
• Reads input using getline() or manual buffer allocation.
• Parses user input into arguments.
• Executes external commands using fork() and execvp().
• Implements a basic command loop (READ -> PARSE -> EXECUTE).

Files and Structure

The project consists of three files:

1. vsh.c

This is the entry point of the shell. It calls the shell() function in a loop until the user decides to exit.

#include <stdio.h>
#include "main.c"

int main(void) {
    int status;
    do {
        status = shell();
    } while (status);
    return 0;
}

2. vsh.h

This header file declares built-in function prototypes and defines constants for token parsing.

#define TOK_DELIM " \t\r\n\a"
#define TOK_SIZE 64

int vsh_cd(char **args);
int vsh_help(char **args);
int vsh_exit(char **args);

3. main.c

This file contains the main logic for:

• Built-in command execution (cd, help, exit)
• Reading user input (getline() or manual input handling)
• Tokenizing input into arguments
• Forking child processes and executing commands
• Main shell loop

Core Functions:

• readLine(): Reads user input from standard input.
• readArgs(): Tokenizes the input into arguments.
• launch(): Forks a child process and executes a command.
• execute(): Checks if the command is built-in; otherwise, launches it as an external command.
• shell(): The main loop that runs the shell.

Compilation and Execution

Compile:

gcc vsh.c -o vsh

Run the Shell:

./vsh

Example Usage

> ls
> mkdir test_dir
> cd test_dir
> pwd
> help
> exit

Notes

• If USE_STD_GETLINE is defined in vsh.h, getline() will be used for input.
• If USE_STD_GETLINE is not defined, manual input handling will be used.

License

This project is open-source and can be modified and distributed freely.