custom-shell

A lightweight shell implementation written in Go that provides basic command execution, history tracking, and file path suggestions.

Features

• Real-time Key Listening: Uses raw terminal mode to capture keystroke, allowing for immediate feedback.

• Interactive History Scroll: Use the Up and Down arrow keys to traverse your command history.

• Signal Awareness: Intercepts Ctrl+C to clear the current buffer or interrupt running processes without crashing the shell.

• Smart Path Suggestions: Provides contextual file/directory hints when typing ls, cat, cd, vim, or nano without arguments.

• Automated Logging: Full audit trail of every command and internal shell state in local/shell.log.

• Tilde Expansion: Automatically converts home directory paths to ~ in the prompt

Project Structure

custom-shell/
├── main.go              # Main entry point
├── go.mod              # Go module definition
├── helpers/            # Helper functions package
│   ├── log.go          # Logging functionality
│   ├── utils.go        # Utility functions (BuildPrefix, CompletePath)
│   ├── history_command.go # History management
│   └── execute_input.go  # Command execution logic
├── local/              # Local storage directory
│   ├── shell.log       # Shell activity logs
│   └── .simple_shell_history # Command history
└── README.md           # This file

Building & Running

Prerequisites

• Go 1.18 or higher
• A terminal supporting ANSI escape codes (Linux/macOS/WSL)

Installation

# Clone the repository and sync dependencies
go mod tidy

# Build the binary
go build -o my-shell

# Run
./my-shell

How It Works

1. Terminal State Management

The shell uses Raw Mode during the input phase. This allows us to detect arrow keys and backspaces instantly. When a command is executed, the shell coordinates with the OS to manage standard input/output streams.

2. The Keyboard Listener

Inside main.go, a continuous listener evaluates keys.Key events:

• Enter: Finalizes the inputBuffer and sends it to the Execution Engine.
• Up/Down Arrows: Triggers MoveBetweenHistoryLines, updating the buffer with previous commands while clearing the current line using ANSI escape codes (\x1b[K).
• Backspace: Manually updates the buffer and handles the visual "erase" on the terminal using \b \b.
• Space/Runes: Appends printable characters to the active buffer.

3. Execution & Signal Handling

When a command runs, the shell creates a signal.NotifyContext. If you press Ctrl+C while a command is running, the shell sends a SIGTERM to the child process only, keeping your shell session alive.

4. Logging: Every step is logged with timestamps to local/shell.log

Package Organization

main.go:

• Initializes logger and shell loop
• Reads user input

helpers/log.go:

• InitLogger() - Setup logging
• LogMsg() - Write timestamped logs
• CloseLogger() - Cleanup

helpers/utils.go:

• BuildPrefix() - Build the shell prompt
• CompletePath() - Get file/directory suggestions

helpers/history_command.go:

• StoreHistory() - Save commands to history file
• ShowHistory() - Display command history
• GetCurrentHistoryLine() - Get last inserted command on history
• MoveBetweenHistoryLines() - Move between the lines of history

helpers/execute_input.go:

• ExecuteInput() - Main command execution logic
• Handles cd, exit, history, and external commands