Badmash Shell 😈

A minimal yet powerful Unix-like shell written in C, featuring command execution, built-in utilities, pipelines, redirections, history support, auto-completion, and a custom lexer/expansion engine.

Badmash Shell is designed as a learning-focused implementation of shell internals --- including parsing, tokenization, execution pipelines, and process management --- while still being practical to use.

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✨ Features

🧠 Core Shell Functionality

• Interactive shell loop using GNU Readline
• Command history support
• Auto-completion for:
  • Built-in commands
  • Executables found in $PATH
• Execution of external programs via execvp
• Background process execution (&)
• Sequential commands using ;

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⚙️ Built-in Commands

Command Description

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echo Print arguments to stdout pwd Print current working directory cd Change directory exit Exit the shell history Display command history type Identify built-in commands or external executables

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🔗 Pipelines

Supports Unix-style pipelines:

ls | grep txt | wc -l

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🔁 Redirection Support

Standard redirections:

>   stdout overwrite
>>  stdout append
<   stdin redirect

Numeric redirections:

2> errors.txt
1>> output.log

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🧾 Lexer & Tokenization

Custom lexer recognizes: - Words - Quotes (' and ") - Escape sequences - Pipes (|) - Semicolons (;) - Background operator (&) - Input/output redirection operators

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🏗️ Execution Engine

• Detects built-ins vs external commands
• Uses fork() + execvp()
• Implements pipelines
• Manages FD redirection
• Supports background execution

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🧱 Project Structure

src/
├── main.c
├── commands.c
├── executor.c
├── shell_lexer.c
└── CMakeLists.txt

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🛠️ Build Instructions

Dependencies

• GCC or Clang
• CMake ≥ 3.13
• GNU Readline development library

Ubuntu/Debian:

sudo apt install build-essential cmake libreadline-dev

Arch:

sudo pacman -S base-devel cmake readline

Fedora:

sudo dnf install gcc cmake readline-devel

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Build

git clone <your-repo-url>
cd <repo>
mkdir build && cd build
cmake ..
make

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Run

./badmash

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👨‍💻 Author

Raz