spf13/cobra

Cobra is a Go library for building structured command-line applications with subcommands, flags, and automatic help generation. The problem it solves is that building a CLI tool in Go from scratch requires a lot of boilerplate: parsing arguments, routing to the right function based on subcommand names, handling flags in a POSIX-compliant way, generating usage text, and supporting shell autocompletion. Cobra packages all of that into a simple, organized framework. In Cobra, you build your CLI by defining Command objects. Each command has a name, a description, an optional list of flags (configuration options like --port or -v), and a run function that executes when the command is invoked. Commands can have child commands, creating a tree that reads naturally: kubectl get pods, git commit --message "fix bug", or hugo server --port 1313. Cobra's pattern encourages CLIs that read like sentences. Once you define your command tree, Cobra automatically generates help text that is displayed when users run --help or invoke an unknown command. It also generates shell autocompletion scripts for bash, zsh, fish, and PowerShell, so users can tab-complete your subcommands and flags. If a user makes a typo, typing app srver instead of app server, Cobra suggests the correct command. Man page generation is built in as well. Cobra integrates with a companion library called Viper for configuration file management, allowing environment variables, config files, and command-line flags to be merged automatically, useful for twelve-factor app patterns. You would use Cobra any time you're building a Go command-line tool beyond a simple single-command program. It is used by some of the most prominent Go projects in existence, Kubernetes (kubectl), Hugo, and the official GitHub CLI (gh) all rely on it. It is installed as a Go module and licensed under Apache 2.0.