Mini Shell

A simple Unix-like shell written in C for learning and experimentation.

Prerequisites

• Linux or macOS with a POSIX userland
• gcc or clang
• make
• C standard: C17; uses POSIX.1-2008 APIs

Quickstart

git clone https://github.com/blazejOz/mini_shell mini_shell
cd mini_shell
cmake -B build
./build/mini_shell

Try it with Docker

You don't need to compile anything to try out mini_shell. You can run the latest version directly from GitHub Packages:

docker run -it --rm ghcr.io/blazejoz/mini_shell:latest

The -it flags are required to interact with the shell's prompt. The --rm flag ensures the container is cleaned up after you exit.

Project Structure

mini_shell/
├── src/                # Source code files
│   ├── main.c          # Entry point of the shell
│   ├── shell.c         # Shell loop and command execution
│   ├── builtins.c      # Implementation of built-in commands
│   ├── parser.c        # Command parsing and tokenization
│   └── utils.c         # Utility functions
├── include/            # Header files
│   ├── shell.h
│   ├── builtins.h
│   ├── parser.h
│   └── utils.h
├── tests/              # Test files
│   ├── test_builtins.c
│   ├── test_parser.c
├── Makefile            # Build instructions
└── README.md           # Project documentation

Features

• Interactive Shell Loop: Robust REPL (Read-Eval-Print Loop) with a clean prompt.
• Advanced Command Pipeline: Supports chaining multiple commands using the | operator.
  • Efficiently handles $N$ processes with $N-1$ concurrent pipes.
  • Proper file descriptor management (uses dup2 for I/O redirection between stages).
  • Synchronous execution: The shell waits for the entire pipeline to complete before returning to the prompt.
• Intelligent Command Dispatcher:
  • Built-in Commands: Executed directly in the parent process (cd, exit, pwd, echo).
  • External Binaries: Discovered via $PATH and executed in forked subshells using execvp.
• Memory Safety: Implements a multi-level cleanup strategy to ensure no memory leaks during parsing or execution.

Roadmap & Planned Features

• Process Pipelines: Concurrent execution of piped commands.
• External Execution: Full integration with system binaries via exec.
• I/O Redirection: Implementing file descriptor hijacking for >, >>, and <.
• Signal Handling: Graceful management of Ctrl+C (SIGINT) and Ctrl+Z (SIGTSTP).
• Variable Expansion: Support for $HOME, $USER, and local shell variables.
• Persistence: Command history saved to ~/.mini_shell_history.

Building

cmake -B build
cmake --build build

Running

./build/mini_shell

Testing

./build/unit_tests

License

MIT License

---

This project is for educational purposes and demonstrates basic shell concepts and system programming in C.