Custom Shell in C

Operating Systems and Networks Project in C.

📑 Table of Contents

1. Project Overview
2. Features
3. Prerequisites
4. Installation & Build
5. Usage
6. Built-in Commands
7. Internal Architecture & Functions
8. Key Implementation Highlights
9. Code Organization
10. Testing
11. Contributing
12. License

📌 Project Overview

This is a Unix-style custom shell implemented in C as an Operating Systems and Networks Project. The shell replicates core functionalities of standard terminals including command parsing, background execution, built-in utilities, job control, history logging, aliasing, piping, redirection, and networked manual pages. It includes modular signal handling, CLI responsiveness, and persistent shell states.

🚀 Features

• Dynamic Prompt — Displays <user@host:cwd> using ~ for home directory
• Built-in Commands — Includes hop, reveal, log, seek, proclore, alias, activities, ping, and a bonus neonate
• Background Process Handling — Signals, exit notifications, job tracking
• External Command Execution — Uses fork and exec, supports & and time tracking
• History Logging — Up to 15 entries, with support for purge and re-execution
• Aliasing — Dynamic alias creation and recall during sessions
• Redirection and Piping — Custom logic for both native and external commands
• Modular Codebase — Clean separation of logic across files
• Signal Safety — Handles ctrl+C, ctrl+Z, and ctrl+D gracefully
• iMan — Fetches formatted man pages via networking sockets
• Bonus: Neonate Mode — Real-time monitoring of system PIDs

📦 Prerequisites

• GCC Compiler (v9.0 or higher recommended)
• Unix/Linux-based OS
• Terminal with POSIX support

⚙️ Installation & Build

make
./a.out

Alternatively:

gcc *.c -o mysh
./mysh

🧪 Usage

Launch the shell using ./a.out. Sample usage:

<user@host:~> hop Documents
<user@host:~/Documents> reveal -la .
<user@host:~/Documents> sleep 5 &
<user@host:~/Documents> log
<user@host:~/Documents> alias ll = reveal -la
<user@host:~/Documents> ping google.com
<user@host:~/Documents> iMan ls

Use ctrl+D to exit safely.

🔧 Built-in Commands

Command	Description
hop	Change directory (~, ., .., -, full path)
reveal	Enhanced ls with color, -a, -l flags
log	View past commands, purge log, or re-execute (log execute n)
proclore	Inspect process details using /proc
seek	Recursive file/directory search with -d for directory-only mode
alias	Define and display dynamic aliases
activities	Show all shell-created background processes
ping	Ping utility from within the shell
neonate	Monitor latest PIDs in real time
iMan	Fetch formatted man pages using sockets

🧠 Internal Architecture & Functions

🗂 Header File

• functions.h — Contains all library includes, globals, and function declarations

🧱 Core Files

• main.c — Initializes shell, calls main loop
• main-logic.c — Handles the core input → parse → execute loop

🔨 Feature Modules

• hop.c — Implements directory navigation
• reveal.c — Custom ls with sorting, coloring, and permission logic
• log.c — Persistent command logging system
• proclore.c — Process inspection from /proc/<pid>
• seek.c — Uses nftw() for recursive search
• alias.c — Dynamic aliasing logic and storage
• activities-ping.c — Background process tracking and signal handling
• neonate.c — Real-time PID monitoring
• networking.c — Fetches and formats man pages (iMan)

⚙️ Utility Modules

• syscom.c — Executes system-level commands via exec
• redirection-piping.c — Implements custom redirection and piping
• misc.c — Time tracking and prompt formatting functions

💡 Key Implementation Highlights

• CLI remains intact even after asynchronous signals
• Logs include errors but ignore commands related to log itself
• Only latest long-running commands get reported with execution time
• Redirection errors from built-in commands are redirected to file
• Aliases are stored dynamically and logged with original command
• Activities are sorted by PID (not lexicographically)
• ctrl+D only triggers exit when no foreground job is active
• Global process array tracks all background shell jobs
• Signal handling ensures child/background processes are cleaned properly

🧩 Code Organization

.
├── Makefile
├── functions.h
├── main.c
├── main-logic.c
├── hop.c
├── reveal.c
├── log.c
├── syscom.c
├── proclore.c
├── seek.c
├── alias.c
├── redirection-piping.c
├── activities-ping.c
├── neonate.c
├── networking.c
├── misc.c

Each module handles a specific functionality to ensure readability and modularity.

✅ Testing

• Sequential and piped command execution
• Foreground and background job management
• Error handling in custom commands
• Alias resolution and redefinition
• Persistent and accurate logging
• Neonate PID monitoring via /proc
• Socket response validation for iMan

🤝 Contributing

Pull requests are welcome!
Please maintain modularity and consistency in naming and structure.
Document all added functions with inline comments.

📄 License

This project is licensed under the MIT License.

---