Environment variable does not overwrite yaml config

[Alex]

Describe the bug
I am trying to have environment variables overwrite something set in my yaml config file however the environment variable does not get set

To Reproduce
Steps / breaking unit test / example to reproduce the behavior

main.go:

package main

import (
	"fmt"
        "log"
	"strings"

	"github.com/knadh/koanf/parsers/yaml"
	"github.com/knadh/koanf/providers/env"
	"github.com/knadh/koanf/providers/file"
	"github.com/knadh/koanf/v2"
)

type Config struct {
	DB     DBConfig `koanf:"db"`
	Key    string   `koanf:"key"`
}

type DBConfig struct {
	Host     string `koanf:"host"`
}

func loadConfig(path string) (config Config, err error) {
	k := koanf.New(".")
	if err = k.Load(file.Provider("config.yml"), yaml.Parser()); err != nil {
		return
	}

	fmt.Println(k.String("db.host"))

	k.Load(env.Provider("MYVAR_", ".", func(s string) string {
		return strings.Replace(strings.ToLower(
			strings.TrimPrefix(s, "MYVAR_")), "_", ".", -1)
	}), nil)

	fmt.Println(k.String("db.host"))

	k.Unmarshal("", &config)
	return
}

func main() {
	config, err := loadConfig(".")
	if err != nil {
		log.Fatal("cannot load config:", err)
	}

You can see in the loadConfig function I have it reading a yaml file, echoing the DB.Host, then reading the env vars, then echoing it again.

config.yml:

db:
    host: localhost

Expected behavior

I set the variable then run the program:

MYVAR_DB_HOST=db_server
go run main.go
// expected output
localhost
db_server - as it would change to the env var
// actual output
localhost
localhost - it did not read the env var

Please provide the following information):

• OS: Linux
• Koanf Version v2

Additional context
I'm aware this is likely me and not a bug :)

[John Behm]

most likely same as #201

[Kailash Nadh]

You're missing export. Should be export MYVAR_DB_HOST=db_server

The program you shared above works.

$ export MYVAR_DB_HOST=xxxx
$ go run main.go
localhost
xxxx

[Alex]

Doh, of course. Thank you