spf13--cobra/cobra

Cobra Generator

Cobra provides its own program that will create your application and add any commands you want. It's the easiest way to incorporate Cobra into your application.

Install the cobra generator with the command go install github.com/spf13/cobra/cobra. Go will automatically install it in your $GOPATH/bin directory which should be in your $PATH.

Once installed you should have the cobra command available. Confirm by typing cobra at a command line.

There are only two operations currently supported by the Cobra generator:

cobra init

The cobra init [app] command will create your initial application code for you. It is a very powerful application that will populate your program with the right structure so you can immediately enjoy all the benefits of Cobra. It can also apply the license you specify to your application.

With the introduction of Go modules, the Cobra generator has been simplified to take advantage of modules. The Cobra generator works from within a Go module.

Initalizing a module

If you already have a module, skip this step.

If you want to initialize a new Go module:

1. Create a new directory
2. cd into that directory
3. run go mod init <MODNAME>

e.g.

cd $HOME/code 
mkdir myapp
cd myapp
go mod init github.com/spf13/myapp

Initalizing an Cobra CLI application

From within a Go module run cobra init. This will create a new barebones project for you to edit.

You should be able to run your new application immediately. Try it with go run main.go.

You will want to open up and edit 'cmd/root.go' and provide your own description and logic.

e.g.

cd $HOME/code/myapp
cobra init
go run main.go

Cobra init can also be run from a subdirectory such as how the cobra generator itself is organized. This is useful if you want to keep your application code separate from your library code.

Optional flags:

You can provide it your author name with the --author flag. e.g. cobra init --author "Steve Francia spf@spf13.com"

You can provide a license to use with --license e.g. cobra init --license apache

Use the --viper flag to automatically setup viper

Viper is a companion to Cobra intended to provide easy handling of environment variables and config files and seamlessly connecting them to the application flags.

Add commands to a project

Once a cobra application is initialized you can continue to use the Cobra generator to add additional commands to your application. The command to do this is cobra add.

Let's say you created an app and you wanted the following commands for it:

• app serve
• app config
• app config create

In your project directory (where your main.go file is) you would run the following:

cobra add serve
cobra add config
cobra add create -p 'configCmd'

cobra add supports all the same optional flags as cobra init does (described above).

You'll notice that this final command has a -p flag. This is used to assign a parent command to the newly added command. In this case, we want to assign the "create" command to the "config" command. All commands have a default parent of rootCmd if not specified.

By default cobra will append Cmd to the name provided and uses this name for the internal variable name. When specifying a parent, be sure to match the variable name used in the code.

Note: Use camelCase (not snake_case/kebab-case) for command names. Otherwise, you will encounter errors. For example, cobra add add-user is incorrect, but cobra add addUser is valid.

Once you have run these three commands you would have an app structure similar to the following:

  ▾ app/
    ▾ cmd/
        config.go
        create.go
        serve.go
        root.go
      main.go

At this point you can run go run main.go and it would run your app. go run main.go serve, go run main.go config, go run main.go config create along with go run main.go help serve, etc. would all work.

You now have a basic Cobra-based application up and running. Next step is to edit the files in cmd and customize them for your application.

For complete details on using the Cobra library, please read the The Cobra User Guide.

Have fun!

Configuring the cobra generator

The Cobra generator will be easier to use if you provide a simple configuration file which will help you eliminate providing a bunch of repeated information in flags over and over.

An example ~/.cobra.yaml file:

author: Steve Francia <spf@spf13.com>
license: MIT
viper: true

You can also use built-in licenses. For example, GPLv2, GPLv3, LGPL, AGPL, MIT, 2-Clause BSD or 3-Clause BSD.

You can specify no license by setting license to none or you can specify a custom license:

author: Steve Francia <spf@spf13.com>
year: 2020
license:
  header: This file is part of CLI application foo.
  text: |
    {{ .copyright }}

    This is my license. There are many like it, but this one is mine.
    My license is my best friend. It is my life. I must master it as I must
    master my life.    

In the above custom license configuration the copyright line in the License text is generated from the author and year properties. The content of the LICENSE file is

Copyright © 2020 Steve Francia <spf@spf13.com>

This is my license. There are many like it, but this one is mine.
My license is my best friend. It is my life. I must master it as I must
master my life.

The header property is used as the license header files. No interpolation is done. This is the example of the go file header.

/*
Copyright © 2020 Steve Francia <spf@spf13.com>
This file is part of CLI application foo.
*/