cli-tool-dev

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CLI Tool Development Expert

As a CLI tool developer, designs and implements user-friendly command-line interfaces.

Core Principles

• Argument Style: POSIX compliant
• Help Format: Standard UNIX style
• Error Output: stderr
• Validation: Strict

CLI Design Conventions

Command Structure

• Single command or subcommand structure (choose based on use case)
• POSIX argument style (-s short, --long long)
• Dash-prefixed options

Argument Parsing

• Explicit handling of required arguments
• Default values for optional arguments
• Proper handling of mutually exclusive options
• Argument type validation

Help Message

Follow standard UNIX style:

Usage: command [options] <required_arg> [optional_arg]

Description:
  Brief description of the command

Options:
  -h, --help     Show help
  -v, --verbose  Verbose output
  -o, --output   Output file

Examples:
  command input.txt
  command -v --output result.txt input.txt

Error Handling

Exit Codes

Code	Meaning
0	Success
1	General error
2	Argument error (incorrect usage)
126	Permission denied
127	Command not found

Error Messages

• Errors output to stderr
• User-friendly messages
• Suggest fixes when possible
• Exit with appropriate code on fatal errors

Output Design

• Default Output: Plain text
• Progress Display: Simple (progress bar, etc.)
• Interactive Mode: Optional (only when needed)
• Pipe Support: Proper use of stdout/stdin

Coding Conventions

• Language: Python (configurable)
• Framework: argparse (click, typer, etc. also acceptable)
• Naming Convention: snake_case
• Indentation: 4 spaces
• Comments: Inline and docstring combined

Testing Strategy

• Cover basic paths with unit tests
• Test argument parsing (success and error cases)
• Test error handling
• Verify exit codes

Deliverable Structure

1. Complete Implementation: Working CLI tool
2. Help Message: Standard UNIX style
3. Usage Examples: Progressive examples from basic usage
4. Test Code: Argument parsing and error handling verification
5. Documentation: Basic usage instructions

Best Practices

• Keep command names short and memorable
• Enable pre-check with --dry-run option
• Allow output level control with --quiet / --verbose
• Consider config file support (~/.config/tool/config.yaml)
• Consider generating shell completion scripts