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@ -22,7 +22,7 @@ Many of the most widely used Go projects are built using Cobra including:
![cobra](https://cloud.githubusercontent.com/assets/173412/10911369/84832a8e-8212-11e5-9f82-cc96660a4794.gif)
## Overview
# Overview
Cobra is a library providing a simple interface to create powerful modern CLI
interfaces similar to git & go tools.
@ -52,21 +52,35 @@ constructors or initialization methods.
Applications built with Cobra commands are designed to be as user-friendly as
possible. Flags can be placed before or after the command (as long as a
confusing space isn’t provided). Both short and long flags can be used. A
command need not even be fully typed. The shortest unambiguous string will
suffice. Help is automatically generated and available for the application or
for a specific command using either the help command or the `--help` flag.
command need not even be fully typed. Help is automatically generated and
available for the application or for a specific command using either the help
command or the `--help` flag.
## Concepts
# Concepts
Cobra is built on a structure of commands & flags.
Cobra is built on a structure of commands, arguments & flags.
**Commands** represent actions and **Flags** are modifiers for those actions.
**Commands** represent actions, **Args** are things and **Flags** are modifiers for those actions.
The best applications will read like sentences when used. Users will know how
to use the application because they will natively understand how to use it.
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
> hugo serve --port=1313
### Commands
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
@ -85,7 +99,7 @@ type Command struct {
}
```
### Flags
## 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](https://golang.org/pkg/flag/).
@ -106,7 +120,7 @@ The tree defines the structure of the application.
Once each command is defined with its corresponding flags, then the
tree is assigned to the commander which is finally executed.
### Installing
# Installing
Using Cobra is easy. First, use `go get` to install the latest version
of the library:
@ -118,14 +132,118 @@ Next, include Cobra in your application:
import "github.com/spf13/cobra"
```
# Getting Started
While you are welcome to provide your own organization, typically a Cobra based
application will follow the following organizational structure.
```
▾ appName/
▾ cmd/
add.go
your.go
commands.go
here.go
main.go
```
In a Cobra app, typically the main.go file is very bare. It serves, one purpose, to initialize Cobra.
```go
package main
import "{pathToYourApp}/cmd"
func main() {
RootCmd.Execute()
}
```
## Using the Cobra Generator
Cobra provides it's own program that will create your application and add any
commands you want. It's the easiest way to incorporate Cobra into your application.
### cobra init
The `cobra init [yourApp]` 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
will also automatically apply the license you specify to your application.
Cobra init is pretty smart. You can provide it a full path, or simply a path
similar to what is expected in the import.
```
cobra init github.com/spf13/newAppName
```
### cobra add
Once an application is initialized Cobra can create additional commands for you.
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'
```
Once you have run these four commands you would have an app structure that would look like:
```
▾ app/
▾ cmd/
serve.go
config.go
create.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.
Obviously you haven't added your own code to these yet, the commands are ready
for you to give them their tasks. 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:
```yaml
author: Steve Francia <spf@spf13.com>
license: MIT
```
## Manually implementing Cobra
To manually implement cobra you need to create a bare main.go file and a RootCmd file.
You will optionally provide additional commands as you see fit.
### Create the root command
The root command represents your binary itself.
#### Manually create rootCmd
Cobra doesn't require any special constructors. Simply create your commands.
Ideally you place this in app/cmd/root.go:
```go
var HugoCmd = &cobra.Command{
var RootCmd = &cobra.Command{
Use: "hugo",
Short: "Hugo is a very fast static site generator",
Long: `A Fast and Flexible Static Site Generator built with
@ -137,11 +255,63 @@ var HugoCmd = &cobra.Command{
}
```
### Create additional commands
You will additionally define flags and handle configuration in your init() function.
Additional commands can be defined.
for example cmd/root.go:
```go
func init() {
cobra.OnInitialize(initConfig)
RootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.cobra.yaml)")
RootCmd.PersistentFlags().StringVarP(&projectBase, "projectbase", "b", "", "base project directory eg. github.com/spf13/")
RootCmd.PersistentFlags().StringP("author", "a", "YOUR NAME", "Author name for copyright attribution")
RootCmd.PersistentFlags().StringVarP(&userLicense, "license", "l", "", "Name of license for the project (can provide `licensetext` in config)")
RootCmd.PersistentFlags().Bool("viper", true, "Use Viper for configuration")
viper.BindPFlag("author", RootCmd.PersistentFlags().Lookup("author"))
viper.BindPFlag("projectbase", RootCmd.PersistentFlags().Lookup("projectbase"))
viper.BindPFlag("useViper", RootCmd.PersistentFlags().Lookup("viper"))
viper.SetDefault("author", "NAME HERE <EMAIL ADDRESS>")
viper.SetDefault("license", "apache")
}
```
### Create your main.go
With the root command you need to have your main function execute it.
Execute should be run on the root for clarity, though it can be called on any command.
In a Cobra app, typically the main.go file is very bare. It serves, one purpose, to initialize Cobra.
```go
package main
import "{pathToYourApp}/cmd"
func main() {
RootCmd.Execute()
}
```
### Create additional commands
Additional commands can be defined and typically are each given their own file
inside of the cmd/ directory.
If you wanted to create a version command you would create cmd/version.go and
populate it with the following:
```go
package cmd
import (
"github.com/spf13/cobra"
)
func init() {
RootCmd.AddCommand(versionCmd)
}
var versionCmd = &cobra.Command{
Use: "version",
Short: "Print the version number of Hugo",
@ -153,12 +323,33 @@ var versionCmd = &cobra.Command{
```
### Attach command to its parent
In this example we are attaching it to the root, but commands can be attached at any level.
If you notice in the above example we attach the command to it's parent. In
this case the parent is the rootCmd. In this example we are attaching it to the
root, but commands can be attached at any level.
```go
HugoCmd.AddCommand(versionCmd)
RootCmd.AddCommand(versionCmd)
```
### Remove a command from its parent
Removing a command is not a common action in simple programs, but it allows 3rd
parties to customize an existing command tree.
In this example, we remove the existing `VersionCmd` command of an existing
root command, and we replace it with our own version:
```go
mainlib.RootCmd.RemoveCommand(mainlib.VersionCmd)
mainlib.RootCmd.AddCommand(versionCmd)
```
## Working with Flags
Flags provide modifiers to control how the action command operates.
### Assign flags to a command
Since the flags are defined and used in different locations, we need to
@ -172,42 +363,24 @@ var Source string
There are two different approaches to assign a flag.
#### Persistent Flags
### Persistent Flags
A flag can be 'persistent' meaning that this flag will be available to the
command it's assigned to as well as every command under that command. For
global flags, assign a flag as a persistent flag on the root.
```go
HugoCmd.PersistentFlags().BoolVarP(&Verbose, "verbose", "v", false, "verbose output")
RootCmd.PersistentFlags().BoolVarP(&Verbose, "verbose", "v", false, "verbose output")
```
#### Local Flags
### Local Flags
A flag can also be assigned locally which will only apply to that specific command.
```go
HugoCmd.Flags().StringVarP(&Source, "source", "s", "", "Source directory to read from")
RootCmd.Flags().StringVarP(&Source, "source", "s", "", "Source directory to read from")
```
### Remove a command from its parent
Removing a command is not a common action in simple programs, but it allows 3rd parties to customize an existing command tree.
In this example, we remove the existing `VersionCmd` command of an existing root command, and we replace it with our own version:
```go
mainlib.RootCmd.RemoveCommand(mainlib.VersionCmd)
mainlib.RootCmd.AddCommand(versionCmd)
```
### Once all commands and flags are defined, Execute the commands
Execute should be run on the root for clarity, though it can be called on any command.
```go
HugoCmd.Execute()
```
## Example