How to make subcommand required in Go CLI using cobra - go

Question

I am using Cobra to make some cli updated to my app. I want to make this command required, meaning the application should fail if it doesn't find the argument it is looking for.
package commands
import (
"github.com/spf13/cobra"
"errors"
"fmt"
)
var (
Env string
)
var RootCmd = &cobra.Command{
Use: "myapp",
Short: "tool",
Long: `tool`,
Run: func(cmd *cobra.Command, args []string) {
// Root command does nothing
},
}
func init() {
RootCmd.AddCommand(Environment)
}
var Environment = &cobra.Command{
Use: "env",
Short: "Specify Environment to run against",
Long: `Can be dev or prod`,
Args: func(cmd *cobra.Command, args []string) error {
if len(args) != 1 {
return errors.New("requires at least one arg")
}
if args[0] == "dev" || args[0] == "prod" {
return nil
}else {
return errors.New("input can only be dev or prod")
}
return fmt.Errorf("invalid env specified: %s", args[0])
},
PreRunE: func(cmd *cobra.Command, args []string) error {
if len(args) != 1 {
return fmt.Errorf("env is required")
}
return nil
},
Run: func(cmd *cobra.Command, args []string) {
Env = args[0]
},
}
and main package is
package main
import (
"fmt"
"log"
"os"
"util"
"commands"
)
func main() {
log.Println("Executing")
if err := commands.RootCmd.Execute(); err != nil {
fmt.Println(err)
os.Exit(1)
}
log.Println("Executing")
}
Now if I run this as ./myApp without any env, it doesn't complain about it. However if I use env after myapp then it activates the function and runs all the validations.

Answer 1

You can just make the body of the function handle it, perhaps by printing help and exiting as non-successful:
Run: func(cmd *cobra.Command, args []string) {
// Root command does nothing
cmd.Help()
os.Exit(1)
},

Answer 2

Omitting the Run (and RunE) field from the cobra.Command will make it a requirement for a valid subcommand to be given:
var RootCmd = &cobra.Command{
Use: "myapp",
Short: "tool",
Long: `tool long help...`,
}
If no subcommand is given on the command line, Cobra will print out the command's Help() text , which will include the root command's Long help text and the autogenerated usage help for all subcommands.