Coral Preamble
I love Cobra and I love Viper. They are great projects, incredibly useful and outstandingly important for the Go community. But sometimes, just sometimes, don't you wish you could use Cobra without the entire dependency chain Viper drags in?
This is what Coral is: a Cobra fork without any of the Viper dependencies and features. This will hopefully be a soft fork with only the minimal changes required to decouple Viper from Cobra. The aim is to follow upstream Cobra development as closely as possible.
Coral has only four direct dependencies:
- github.com/spf13/pflag
- github.com/cpuguy83/go-md2man/v2
- github.com/inconshreveable/mousetrap
- gopkg.in/yaml.v2
Migrating existing projects to Coral
It's easy to use Coral as a drop-in replacement for Cobra in existing projects, just let gofmt do the heavy lifting for you:
gofmt -w -r '"github.com/spf13/cobra" -> "github.com/muesli/coral"' .
gofmt -w -r '"github.com/spf13/cobra/doc" -> "github.com/muesli/coral/doc"' .
gofmt -w -r 'cobra -> coral' .
go mod tidy
As a result, you should typically see a lot of indirect dependencies removed from the project's go.mod and go.sum files.
Upstream Cobra README
Cobra is both a library for creating powerful modern CLI applications as well as a program to generate applications and command files.
Cobra is used in many Go projects such as Kubernetes, Hugo, and Github CLI to name a few. This list contains a more extensive list of projects using Cobra.
Overview
Cobra is a library providing a simple interface to create powerful modern CLI interfaces similar to git & go tools.
Cobra is also an application that will generate your application scaffolding to rapidly develop a Cobra-based application.
Cobra provides:
- Easy subcommand-based CLIs:
app server,app fetch, etc. - Fully POSIX-compliant flags (including short & long versions)
- Nested subcommands
- Global, local and cascading flags
- Easy generation of applications & commands with
cobra init&cobra add cmdname - Intelligent suggestions (
app srver... did you meanapp server?) - Automatic help generation for commands and flags
- Automatic help flag recognition of
-h,--help, etc. - Automatically generated shell autocomplete for your application (bash, zsh, fish, powershell)
- Automatically generated man pages for your application
- Command aliases so you can change things without breaking them
- The flexibility to define your own help, usage, etc.
- Optional seamless integration with viper for 12-factor apps
Concepts
Cobra is built on a structure of commands, arguments & flags.
Commands represent actions, Args are things and Flags are modifiers for those actions.
The best applications read like sentences when used, and as a result, users intuitively know how to interact with them.
The pattern to follow is APPNAME VERB NOUN --ADJECTIVE. or APPNAME COMMAND ARG --FLAG
A few good real world examples may better illustrate this point.
In the following example, 'server' is a command, and 'port' is a flag:
hugo server --port=1313
In this command we are telling Git to clone the url bare.
git clone URL --bare
Commands
Command is the central point of the application. Each interaction that the application supports will be contained in a Command. A command can have children commands and optionally run an action.
In the example above, 'server' is the command.
Flags
A flag is a way to modify the behavior of a command. Cobra supports fully POSIX-compliant flags as well as the Go flag package. A Cobra command can define flags that persist through to children commands and flags that are only available to that command.
In the example above, 'port' is the flag.
Flag functionality is provided by the pflag library, a fork of the flag standard library which maintains the same interface while adding POSIX compliance.
Installing
Using Cobra is easy. First, use go get to install the latest version of the library. This command will install the cobra generator executable along with the library and its dependencies:
go get -u github.com/spf13/cobra
Next, include Cobra in your application:
import "github.com/spf13/cobra"
Usage
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.
For complete details on using the Cobra generator, please read The Cobra Generator README
For complete details on using the Cobra library, please read the The Cobra User Guide.
License
Cobra is released under the Apache 2.0 license. See LICENSE.txt
