104 lines
4.1 KiB
Markdown
104 lines
4.1 KiB
Markdown
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Cobra is both a library for creating powerful modern CLI applications as well as a program to generate applications and command files.
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Cobra is used in many Go projects such as [Kubernetes](http://kubernetes.io/),
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[Hugo](https://gohugo.io), and [Github CLI](https://github.com/cli/cli) to
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name a few. [This list](./projects_using_cobra.md) contains a more extensive list of projects using Cobra.
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[](https://github.com/spf13/cobra/actions?query=workflow%3ATest)
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[](https://godoc.org/github.com/spf13/cobra)
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[](https://goreportcard.com/report/github.com/spf13/cobra)
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[](https://gophers.slack.com/archives/CD3LP1199)
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# Overview
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Cobra is a library providing a simple interface to create powerful modern CLI
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interfaces similar to git & go tools.
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Cobra is also an application that will generate your application scaffolding to rapidly
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develop a Cobra-based application.
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Cobra provides:
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* Easy subcommand-based CLIs: `app server`, `app fetch`, etc.
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* Fully POSIX-compliant flags (including short & long versions)
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* Nested subcommands
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* Global, local and cascading flags
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* Easy generation of applications & commands with `cobra init appname` & `cobra add cmdname`
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* Intelligent suggestions (`app srver`... did you mean `app server`?)
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* Automatic help generation for commands and flags
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* Automatic help flag recognition of `-h`, `--help`, etc.
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* Automatically generated shell autocomplete for your application (bash, zsh, fish, powershell)
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* Automatically generated man pages for your application
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* Command aliases so you can change things without breaking them
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* The flexibility to define your own help, usage, etc.
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* Optional tight integration with [viper](http://github.com/spf13/viper) for 12-factor apps
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# Concepts
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Cobra is built on a structure of commands, arguments & flags.
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**Commands** represent actions, **Args** are things and **Flags** are modifiers for those actions.
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The best applications read like sentences when used, and as a result, users
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intuitively know how to interact with them.
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The pattern to follow is
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`APPNAME VERB NOUN --ADJECTIVE.`
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or
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`APPNAME COMMAND ARG --FLAG`
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A few good real world examples may better illustrate this point.
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In the following example, 'server' is a command, and 'port' is a flag:
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hugo server --port=1313
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In this command we are telling Git to clone the url bare.
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git clone URL --bare
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## Commands
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Command is the central point of the application. Each interaction that
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the application supports will be contained in a Command. A command can
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have children commands and optionally run an action.
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In the example above, 'server' is the command.
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[More about cobra.Command](https://godoc.org/github.com/spf13/cobra#Command)
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## Flags
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A flag is a way to modify the behavior of a command. Cobra supports
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fully POSIX-compliant flags as well as the Go [flag package](https://golang.org/pkg/flag/).
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A Cobra command can define flags that persist through to children commands
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and flags that are only available to that command.
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In the example above, 'port' is the flag.
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Flag functionality is provided by the [pflag
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library](https://github.com/spf13/pflag), a fork of the flag standard library
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which maintains the same interface while adding POSIX compliance.
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# Installing
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Using Cobra is easy. First, use `go get` to install the latest version
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of the library. This command will install the `cobra` generator executable
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along with the library and its dependencies:
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go get -u github.com/spf13/cobra
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Next, include Cobra in your application:
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```go
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import "github.com/spf13/cobra"
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```
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# Usage
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See [User Guide](user_guide.md).
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# License
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Cobra is released under the Apache 2.0 license. See [LICENSE.txt](https://github.com/spf13/cobra/blob/master/LICENSE.txt)
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