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UNDER CONSTRUCTION

ASTRA Shell is a Linux-compatible Unix shell written in C++ that implements core POSIX shell features including job control, signal handling, process groups, foreground/background execution, and pipelines.

This project was built incrementally to understand how real shells interact with the kernel, focusing on correctness over convenience.

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Features Implemented

Core Shell

• Interactive prompt (astra$)
• Command execution via fork() + execvp()
• PATH-based command lookup
• Graceful shell exit

Built-in Commands

• cd [dir] — change directory
• pwd — print current directory
• jobs — list active jobs
• fg %n — bring job to foreground
• bg %n — resume job in background
• exit — exit the shell

Job Control (POSIX-Correct)

• Foreground and background execution (&)
• Process groups (PGID-based job tracking)
• Terminal ownership management via tcsetpgrp
• Correct handling of:
  • Ctrl+C → terminate foreground job
  • Ctrl+Z → stop foreground job
• Resume stopped jobs using fg / bg
• Zombie-free execution

Signal Handling

• Shell ignores interactive signals (SIGINT, SIGTSTP, SIGTTOU, SIGTTIN)
• Child processes restore default signal behavior
• SIGCHLD handled safely (no logic inside handlers)

Pipelines

• Arbitrary-length pipelines using |
• Correct stdin/stdout redirection via pipe() and dup2()
• Entire pipeline treated as one job
• Pipelines fully support:
  • Ctrl+C
  • Ctrl+Z
  • fg / bg
  • background execution

Example:

ls | grep cpp | wc -l

Build & Run

Requirements :

• Linux or WSL2
• C++17 compatible compiler
• POSIX environment

Build

mkdir build
cd buid
cmake ..
make

Run

./astra

Not Yet Implemented

• I/O redirection (> < >> 2>)
• Environment variables (export, $VAR)
• Command history / line editing
• /proc-based memory awareness (planned)
• Scripting support

Motivation

ASTRA Shell was built as a systems programming exercise to deeply understand:

• Unix process model
• Job control internals
• Terminal behavior
• Signal semantics

How real shells like bash actually work