MiniShell - A Modern Shell Implementation in C#

A fully-featured shell built from scratch in C#/.NET, featuring advanced input handling, tab completion with trie-based prefix matching, persistent command history, I/O redirection, and pipeline support.

📖 Read the technical deep dive on my blog! Learn about the architecture decisions, implementation challenges, and lessons learned while building this shell.

Key Features

• Trie-based tab completion with intelligent prefix matching
• Full readline-style input with arrow key navigation and history
• Persistent command history with HISTFILE support
• Cross-platform PATH resolution for Windows and Unix
• Dependency injection architecture for testability
• I/O redirection with automatic directory creation

Supported Features

• Built-in commands: cd, pwd, echo, type, exit, greet, history
• Tab completion: Smart prefix matching with trie data structure
• Command history: Persistent history with arrow key navigation
• I/O redirection: >, >>, 2>, 2>>
• Pipelines: Multi-command pipelines with |
• External commands: PATH resolution with cross-platform support

Quick Start

Prerequisites

• .NET 9.0 SDK

Running the Shell

dotnet run

Or use the provided script:

./your_program.sh

Demos

Tab Completion

Command History

$ echo "first command"
$ echo "second command"
# Press UP arrow to navigate through history
$ history
    1  echo "first command"
    2  echo "second command"
$ history -w ~/.minishell_history  # Save history to file

I/O Redirection

$ echo "hello world" > output.txt
$ echo "line 2" >> output.txt  # Append mode
$ ls /nonexistent 2> errors.txt  # Redirect stderr
$ echo "test" > /tmp/deep/path/file.txt  # Auto-creates directories

Pipelines

$ echo "hello world" | tr 'a-z' 'A-Z'
HELLO WORLD
$ cat file.txt | grep "pattern" | wc -l
3

Built-in Commands

$ pwd
/home/user
$ cd /tmp
$ echo hello world
hello world
$ type cd
cd is a shell builtin
$ greet
Hello, World!

Application Flow

View the detailed mermaid diagram

Project Structure

src/
├── Program.cs                    # DI setup and entry point
├── Shell/
│   ├── Shell.cs                 # REPL orchestrator
│   ├── CommandRouter.cs         # Command parsing and routing
│   └── PipelineExecutor.cs      # Pipeline execution
├── Commands/                     # Built-in command implementations
├── Runtime/
│   ├── CustomInputHandler.cs    # Readline-style input handler
│   ├── HistoryService.cs        # Persistent history
│   ├── PathResolver.cs          # Cross-platform PATH lookup
│   └── FileRedirectionHandler.cs # I/O redirection
├── Parsing/
│   ├── ShellTokenizer.cs        # Input tokenization
│   ├── PipelineParser.cs        # Pipeline parsing
│   └── RedirectionParser.cs     # Redirection parsing
├── DataStructures/
│   └── CompletionTrie.cs        # Tab completion trie
└── Abstractions/                 # Interfaces for testability

Testing

dotnet test

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Built as part of CodeCrafters "Build Your Own Shell" Challenge.