Adding a subcommand

So now lets add an easy subcommand - sum, to make our CLI function like this:

math sum 1 2 3
>6

We'll use cobra-cli to add a new subcommand to the rootCmd, and save us from having to write out the new *cobra.Command ourselves. Run this from the root of your source code repository.

cobra-cli add sum

You should now see a new file, cmd/sum.go, in place:

.
├── LICENSE
├── cmd
│   ├── root.go
│   └── sum.go  <-- new!
├── go.mod
├── go.sum
├── main.go
└── math

Open this file, and take a look at the init() function declaration:

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

This is where we start building our tree of commands. Here we've taken rootCmd and added the new sumCmd to it as a subcommand. Our tree looks something like this:

If you build and run your project now, you'll see our help output has changed.

$ go build -o math . && ./math
Execute fun math functions

Usage:
  math [command]

Available Commands:
  completion  Generate the autocompletion script for the specified shell
  help        Help about any command
  sum         A brief description of your command

Flags:
  -h, --help     help for math
  -t, --toggle   Help message for toggle

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

We now have our sum command with its (Short) description, as well as some flag definitions (more to come on those later, it was scaffolded by cobra-cli and I've ignored it so far), and generic subcommands like help. You now also see a Usage statement.

Now, you can also run the math sum command. Try that now.

$ ./math sum
sum called

Practice:

If you're following along, go ahead and practice what we did with the root command: Change the Short and Long descriptions for the sumCmd to indicate that we will take an arbitrary number of integers and return the sum of their values.