Adding subcommands to subcommands

So far, we've add the subtract and sum subcommands to the math root command. But it's possible to also add subcommands to other subcommands.

Let's build a subcommand that logically groups subtract and add, called arithmetic. Let's break out cobra-cli to build out the base subcommand arithmetic.

$ cobra-cli add arithmetic
arithmetic created at /Users/me/.go/src/github.com/opdev/cobra-primer/math

With this in place, let's go ahead and disable the Run function so that calling math arithmetic just displays help output.

var arithmeticCmd = &cobra.Command{
	Use:   "arithmetic",
	Short: "basic arithmetic functions",
}

To move sum and subtract to be organized under arithmetic instead of the root command math, just open sum.go and subtract.go to their init() functions, and replace rootCmd.AddCommand with arithmeticCmd.AddCommand.

Here's what subtract.go's init function looks like now:

func init() {
	arithmeticCmd.AddCommand(subtractCmd)
	subtractCmd.Flags().BoolP("invert-sign", "i", false, "inverts the sign of the result.")
}

And our command "tree" went from this:

to this:

And our commands are logically grouped with the arithmetic subcommand:

$ go build . && ./math arithmetic --help
basic arithmetic functions

Usage:
  math arithmetic [command]

Available Commands:
  subtract    subtract integers
  sum         add integers

Flags:
  -h, --help   help for arithmetic

Use "math arithmetic [command] --help" for more information about a command.

If you were scaffolding a net-new command using cobra-cli and you wanted it organized under some command OTHER than the root command, you can pass the --parent flag to cobra-cli which will organize the new command under the new parent.