macOS Terminal Simulator

A lightweight terminal simulator written in C that mimics basic shell commands such as ls, cd, mkdir, touch, rm, cat, edit, and more using a custom tree-based virtual filesystem synced with the real local filesystem.

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Features

• Terminal Prompt: Interactive command-line prompt reflecting current directory pathing.
• Modular Codebase: Highly organized into clear source and header modules separating CLI, virtual filesystem, and generic utilities.
• On-Demand VFS Lazy Loading: Efficiently crawls and synchronizes local filesystem directories only when they are accessed.
• Access Diagnostics: Provides standard POSIX warnings when trying to traverse permission-restricted directories.
• Colored Terminal Output: Enhanced readability using tailored ANSI color palettes.
• Simulated File Permission Engine: Interactive chmod command to control simulated node permissions.
• Built-in Interactive Editor: Supports editing virtual file contents on the fly.
• Command History: Tracks and displays history of entered commands.

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Supported Commands

Command	Description
help	Show all commands
ls	List files and folders
tree	Display directory tree
pwd	Show current directory
cd <dir>	Change directory
mkdir <dir>	Create directory
touch <file>	Create file
rm <path>	Remove file or directory
cat <file>	Display file content
edit <file>	Edit file content
chmod <mode> <file>	Change simulated permissions
history	Show command history
clear	Clear terminal
finder	Open current folder in Finder
exit	Exit simulator

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Project Structure

The codebase is refactored into modular components for clean separation of concerns:

├── common.h         # Color ANSI escape constants and global configuration
├── utils.h          # String utility and timestamp declarations
├── utils.c          # Tokenizer functions, path splitting/joining, and timer implementation
├── fs.h             # Virtual Filesystem (VFS) declarations and tree structure
├── fs.c             # Core VFS logic, dynamic lazy loading, and POSIX sync implementation
├── main.c           # Front-end CLI program entry point and interactive shell loop
├── Makefile         # Compiler and linker rules for gcc
└── README.md        # Technical project documentation

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🚀 Step-by-Step Guide: Compile & Run

Follow these commands in your standard system terminal to build and run the project:

1. Clone the repository

git clone https://github.com/ShivaanjayNarula/Terminal.git
cd Terminal

2. Open Workspace

Make sure your terminal is located in the root directory of the project:

3. Compile the Project

Build the modular modules into the unified terminal_simulator binary:

make

4. Launch the Simulator

Start the interactive simulator shell:

./terminal_simulator

5. (Optional) Reset/Clean Build Outputs

To reset the build environment by removing compiled .o object files and the generated binary, run:

make clean

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🧠 How It Works

Virtual Filesystem (VFS) Tree Structure

The simulator maintains an in-memory, tree-based directory model using linked node structures:

typedef struct TreeNode {
    char* name;
    char type;                // 'd' (directory) or '-' (file)
    int perm;                 // Simulated octal permission (0-7)
    char* cdate;              // Creation timestamp
    char* mdate;              // Modification timestamp
    StringArray content;      // Virtual file text line contents
    struct TreeNode* parent;
    struct TreeNode* child;
    struct TreeNode* link;
} TreeNode;

On-Demand Lazy Loading (Dynamic Synchronization)

• The Problem: A full recursive crawl of / at startup would traverse millions of files, causing gigabytes of RAM usage, severe startup delays, or Out-Of-Memory system crashes.
• The Solution: On startup, the simulator loads a shallow skeleton of the filesystem up to a depth of 2 (/, /Users, and /Users/<username>). As you navigate (cd), list (ls), or manipulate paths (mkdir, touch), the core VFS dynamically invokes POSIX APIs (opendir, readdir) to scan and populate child directories on-demand under the corresponding tree nodes. This keeps startup instant while allowing full path exploration!

Directory Protection (Access Diagnostics)

Modern macOS versions restrict terminal applications from accessing personal folders (e.g., Documents, Desktop, Downloads) without explicit "Full Disk Access" permissions. If the simulator processes attempt to load a protected directory without these privileges, the VFS diagnoses the POSIX failure and prints an elegant warning:

Permission denied: Cannot access '/Users/shivaanjaynarula/Documents'

Publicly readable folders (like Public) are synchronized dynamically and can be listed without permission issues.

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Example Usage Flow

Run the following commands inside the simulator prompt:

user@terminal:/$ cd Users/shivaanjaynarula/Public
user@terminal:/Users/shivaanjaynarula/Public$ ls
drwx Drop Box/
user@terminal:/Users/shivaanjaynarula/Public$ mkdir test_directory
user@terminal:/Users/shivaanjaynarula/Public$ cd test_directory
user@terminal:/Users/shivaanjaynarula/Public/test_directory$ touch note.txt
user@terminal:/Users/shivaanjaynarula/Public/test_directory$ edit note.txt
# Enter text and type \n to save
user@terminal:/Users/shivaanjaynarula/Public/test_directory$ cat note.txt
user@terminal:/Users/shivaanjaynarula/Public/test_directory$ tree
user@terminal:/Users/shivaanjaynarula/Public/test_directory$ cd ..
user@terminal:/Users/shivaanjaynarula/Public$ rm test_directory/note.txt
user@terminal:/Users/shivaanjaynarula/Public$ rm test_directory
user@terminal:/Users/shivaanjaynarula/Public$ exit

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Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Test thoroughly
5. Submit a pull request

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License

This project is licensed under the GNU Affero General Public License v3.0.

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