spf13-cobra

spf13/cobra examples

• URL: https://github.com/spf13/cobra
• godoc: https://godoc.org/github.com/spf13/cobra

cobra generator installation

The cobra generator is not installed with go get (on Windows at least), to build and install:

1. go get github.com\spf13\viper.
2. go get github.com/mitchellh/go-homedir.
3. Navigate to GOPATH\src\github.com\spf13\cobra\cobra (note the second cobra directory).
4. go install.

Generating sample app

Run cobra init github.com/blah/whatever to create the structure for an app. The directory will be created under src. So in this case I ran cobra init Go-Security/cli-package-tests/spf13-cobra/app.

If not specified, the default LICENSE is Apache v2. Replace it with your own license if needed.

We can configure author and license with flags: cobra init app -l MIT -a "Parsia".

main.go

Main just calls cmd.Execute() which is in app/cmd/root.go.

cmd/root.go

Inside root.go we can define what the application does when nothing is passed to it.

var rootCmd = &cobra.Command{
    Use:   "cobra-example",
    Short: "Sample app to learn Cobra",
    // Long is printed with -h
    Long: `Sample app to learn Cobra.
Second line.`,
    // Uncomment the following line if your bare application
    // has an action associated with it:
    // Here we can pass our own function for noArgs.
    Run: noArgs,
}

// noArgs is run if program is run without arguments.
func noArgs(cmd *cobra.Command, args []string) {
    fmt.Println("please provide some arguments")

    // Print usage string
    fmt.Println(cmd.UsageString())
}

Cobra by default adds support to read info from cfg files using Viper.

cmd/cmd1.go

This will be created if we do cobra add cmd1. We can set the description and other info for the cmd here. We can create aliases here by creating a string slice.

// cmd1Cmd represents the cmd1 command
var cmd1Cmd = &cobra.Command{
    Use:   "cmd1",
    Short: "Short description of cmd1",
    Long:  `Long description of cmd1`,
    // cmd1 aliases
    Aliases: []string{"cmd11", "cmd12"},
    Run:     cmd1Executor,
}

// cmd1Executor is run when cmd1 is called.
func cmd1Executor(cmd *cobra.Command, args []string) {
    // Here we can see what command was run and also any arguments.
    fmt.Println("cmd1 called")
    // Print arguments after cmd1
    fmt.Println("arguments", args)
}

We can call cmd or any of the aliases and access the arguments after it.

$ go run main.go cmd11
cmd1 called

$ go run main.go cmd12
cmd1 called

$ go run main.go cmd1 arg1 arg2
cmd1 called
arguments [arg1 arg2]

cmd2.go

We create cmd2 and assign cmd1 as its parent. cobra add cmd2 -p "cmd1Cmd". Note cmd1Cmd is correct and not cmd1. To get the name of the command, go to cmd1.go and look inside init():

func init() {
    rootCmd.AddCommand(cmd1Cmd)
}

If this happens, modify the init function inside cmd2.go:

func init() {
    cmd1Cmd.AddCommand(cmd2Cmd)
}

Now we can run cmd2 as a subcommand of cmd1.

$ go run main.go cmd1 cmd2
cmd2 called

And it shows up in cmd1's help.

$ go run main.go cmd1 -h
Long description of cmd1

Usage:
  cobra-example cmd1 [flags]
  cobra-example cmd1 [command]

Aliases:
  cmd1, cmd11, cmd12

Available Commands:
  cmd2        Short description of cmd2

Flags:
  -h, --help   help for cmd1

Global Flags:
      --config string   config file (default is $HOME/.app.yaml)

Use "cobra-example cmd1 [command] --help" for more information about a command.