building-clis

Use Typer for new Python CLIs: define commands with decorators and type hints, which provide automatic validation and help text. Install with pip install "typer[all]" to include rich for colored output, then distribute via PyPI with a console_scripts entry point in pyproject.toml.

Use Cobra for enterprise tools with complex subcommand hierarchies and Viper configuration integration—it powers Kubernetes, Docker, and the GitHub CLI. Choose urfave/cli for simple utilities with 5-10 commands where minimal boilerplate matters.

Standard precedence from highest to lowest: CLI arguments, environment variables, local config file, user config file (~/.config/app/), system config file (/etc/), then built-in defaults. Document this order in help text and provide a command to show the effective merged configuration.

Typer generates completions via environment variables like _MYAPP_COMPLETE=bash_source. Cobra provides GenBashCompletion and GenZshCompletion methods exposed through a completion subcommand. Rust's clap uses the clap_complete crate to generate scripts for bash, zsh, fish, and PowerShell.

Use positional arguments for primary required inputs, limited to 2-3 maximum. Use named options for configuration values and optional inputs, and boolean flags for toggles like --verbose or --dry-run. More than three positional arguments becomes confusing and should be converted to named options.

Publish to crates.io with cargo publish so users can run cargo install, or build cross-platform binaries with GitHub Actions and attach them to releases. You can also create a Homebrew formula that builds from source using cargo install.