Go Cobra Environment Mapping Example

main.go

package main

import (
	"context"
	"fmt"
	"strings"

	"github.com/spf13/cobra"
	"github.com/spf13/pflag"
	"github.com/spf13/viper"
)

var (
	cmd = &cobra.Command{
		Use:  "goprompt",
		RunE: cmdExecute,
	}
)

func init() {
	cmd.Flags().Int(
		"cmd-status", 0, "cmd status of previous command",
	)
	cmd.Flags().Int(
		"pre-exec-ts", 0, "pre-execution timestamp to gauge how log execution took",
	)
	cmd.PersistentPreRunE = func(cmd *cobra.Command, args []string) error {
		return bindEnvironmentFlags(cmd, "prefix")
	}
}

func bindEnvironmentFlags(cmd *cobra.Command, prefix string) error {
	v := viper.New()

	// Prep environment mapping.
	v.SetEnvPrefix(prefix)
	v.SetEnvKeyReplacer(strings.NewReplacer("-", "_"))
	v.AutomaticEnv()

	// Bind flagset and read in config.
	if err := v.BindPFlags(cmd.Flags()); err != nil {
		return err
	}
	if err := v.ReadInConfig(); err != nil {
		return err
	}

	cmd.Flags().VisitAll(func(f *pflag.Flag) {
		if !f.Changed && v.IsSet(f.Name) {
			cmd.Flags().Set(f.Name, fmt.Sprintf("%v", v.Get(f.Name)))
		}
	})
	return  nil
}

func cmdExecute(cmd *cobra.Command, args []string) error {
	return nil
}

func main() {
	err := cmd.ExecuteContext(context.Background())
	if err != nil {
		panic(err)
	}
}