MiniShell

Overview

MiniShell is a user-friendly yet extensible POSIX shell written in modern C++. It offers a clean interface, familiar syntax, and essential features like alias handling, variable expansion, command substitution, globbing, pipelines, and optional Readline integration.

Highlights

• Written in C++17 with modular headers.
• Built-in support for environment variable and command substitution, alias expansion, and globbing.
• Minimal yet extensible job control with background and foreground management.
• Customizable prompt with status colorization and optional Git branch information.
• Optional integration with Readline for command history and line editing.
• Automatic generation of a .minishellrc file for configuration.

Project Structure

minishell/
├── main.cpp                  # Core REPL and process management
├── minishell_colors.hpp      # ANSI color definitions and helpers
├── minishell_tokenize.hpp    # Tokenizer handling quotes and escapes
├── minishell_expand.hpp      # Scalar and glob expansion, command substitution
├── minishell_jobs.hpp        # Job control and signal handling
├── minishell_builtins.hpp    # Built-in commands logic
├── minishell_prompt.hpp      # Prompt construction with Git info
├── build.sh                  # Cross-distro build helper script
└── install.sh                # Installer and .minishellrc generator

Features

• POSIX compliance: uses standard system calls (fork, execvp, dup2, pipe, waitpid) for reliability.
• Built-in commands: implements cd, pwd, echo, export, unset, alias, unalias, source, along with simple auto-CD logic (changing into a directory when typed without explicit cd).
• Pipelines and redirection: supports multiple stages of pipes (|), input (<), output (>), and append (>>) redirection.
• Variable and command substitution: expands variables ($VAR, ${VAR}), command substitution using backticks or $( ... ), and tilde expansion (~ to $HOME).
• Globbing: expands wildcard patterns using the glob library.
• Alias expansion: user-defined aliases can replace the first word of a command.
• Job control: background jobs (command &), jobs, fg, and bg commands.
• Readline integration: optional build with Readline for interactive editing and history.

Prerequisites

To build and run MiniShell, you need:

• A C++17-capable compiler (e.g., GCC or Clang).
• CMake (version 3.10 or later).
• pkg-config for locating dependencies.
• Optionally: readline and ncurses (for interactive features), and Ninja (for faster builds).
• A POSIX-compliant environment. Windows is not supported at this time.

Building from Source

Use the provided build.sh script. It detects your system's package manager, installs missing dependencies (if possible), configures CMake, and builds the binary.

# Default debug build with sanitizers and Readline if available
./build.sh

# Release build
./build.sh -R

# Build without Readline support
./build.sh --no-readline

# Disable ASan and UBSan (debug build)
./build.sh --no-sanitizers

# Build and run automatically
./build.sh --run

# Clean build directory
./build.sh --clean

You can override the compiler by setting CC and CXX before running the script:

CC=clang CXX=clang++ ./build.sh -R

Installation

Use the install.sh script to compile and install MiniShell. It will build the project if necessary, copy the executable, create a configuration file, and back up any existing .minishellrc.

# Install to /usr/local/bin (requires sudo)
./install.sh

# Install to ~/.local/bin (no sudo)
./install.sh --user

During installation, the script will:

• Compile MiniShell if a build is not already available.
• Install the binary to /usr/local/bin or ~/.local/bin.
• Generate a default ~/.minishellrc file with example aliases and environment variables.
• Backup any existing ~/.minishellrc to ~/.minishellrc.bak.

About the .minishellrc File

After installation, a configuration file is placed at ~/.minishellrc. It behaves similarly to .bashrc or .zshrc and is executed at startup. The generated file contains helpful examples:

# ~/.minishellrc — generated by minishell installer

# --- Welcome ---
echo "Welcome to MiniShell, $USER!"

# --- Aliases ---
alias ll='ls -lah --color=auto'
alias gs='git status'
alias please='sudo !!'

# --- Environment ---
export EDITOR=nano
export LANG=en_US.UTF-8
export PAGER=less

# --- Prompt override (optional) ---
# setprompt "λ $USER terminal → "

Feel free to modify or extend this file. You can define additional aliases, environment variables, or adjust the prompt text to your liking.

Usage Examples

After launching MiniShell, you can use it like a regular shell:

Print a message:

λ user terminal → echo hello
hello

Use an alias:

λ user terminal → ll
total 8
-rw-r--r-- 1 user user 1234 ... main.cpp
...

Change directories:

λ user terminal → cd /etc
λ user terminal → pwd
/etc

Read environment variables:

λ user terminal → echo $HOME
/home/user

Apply globbing and pipelines:

λ user terminal → cat *.hpp | grep class
class BuiltinEnv {
    ...

Supported Constructs

MiniShell supports:

• Alias expansion for the first word of a command.
• Environment variable substitution ($VAR, ${VAR}).
• Command substitution using backticks and $( command ).
• Globbing via *, ?, and character ranges.
• Multi-stage pipelines with | and I/O redirection.
• Basic job control: run jobs in the background with &, list jobs with jobs, move to the foreground with fg, or background with bg.

Known Limitations

• Command auto-completion is not implemented yet.
• Nested command substitution (e.g., $(echo $(pwd))) is not fully supported.
• Job control does not fully restore TTY modes in complex scenarios.
• Windows is not supported; a POSIX environment is required.

Development Notes

• The codebase is modular. Each .hpp header is self-contained and can be edited independently.
• Build with ENABLE_SANITIZERS=ON to help detect memory issues during development.
• Enable WITH_READLINE=ON when debugging interactive features.
• You can customize your development prompt through setprompt in your .minishellrc.

Roadmap

Version	Planned Features
v1.0.0	Stable interactive shell core
v1.1.0	Autocompletion via Readline
v1.2.0	Syntax highlighting
v1.3.0	Plugin system (~/.minishell/plugins/)
v1.4.0	History persistence
v2.0.0	Theming and compatibility with Oh-My-Zsh

Contributing

Contributions are welcome. If you find a bug, have feature suggestions, or want to get involved, follow these steps:

1. Fork the repository on GitHub.
2. Clone your fork and make your changes in a branch.
3. Use the build.sh script to compile and test locally.
4. Open a pull request with a clear description of your changes.

Please include tests or examples where applicable. We appreciate contributions of all kinds, from documentation improvements to new features.

License

This project is licensed under the MIT License. You are free to use, modify, and distribute MiniShell. See the LICENSE file for full details.

Acknowledgments

MiniShell is inspired by Bash, Zsh, and other Unix shells. It leverages open-source libraries such as Readline, Ncurses, and CMake. Special thanks to the open-source community for providing these building blocks.