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Published: Jul 21, 2022 License: MIT Imports: 11 Imported by: 0


Declarative configuration for Go 🚀

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  • declarative way of defining configuration
  • reading configuration from file, environment variables or command line arguments in one lines of code
  • validation


config is a package that supports reading configuration into a struct from files, environment variable and command line arguments. All you need is to declare a config structure and call Read method.

package main

import (


type Config struct {
	DB        Database `default:{}`
	DebugMode bool     `flag:"debug"`

type Database struct {
	Host     string `default:"localhost" validate:"required"`
	Password string `validate:"required"`
	DbName   string `default:"mydb"`
	Username string `default:"root"`
	Port     int    `default:"5432"`

func main() {
	var conf Config
	err := config.NewConfReader("myconf").Read(&conf)
	if err != nil {

	fmt.Printf("Config %+v", conf)

When you want to change, for example, DB Host of your applications you can do any of the following:

  1. create config myconf.yaml file in home directory
   host: "localhost"
  1. set environment variable. Like DB_HOST=localhost
  2. set command line argument. Like

ℹ️ Refer to the example that illustrates how to use ConfReader.

Execute go run examples/main.go to run the example.

Install 📦
go get  

Setting Configuration Values 👷

ConfReader merges values from all three sources in the following order:

  1. File
  2. Environment variables
  3. Command line arguments

Setting same key in file will be overridden by environment variable and command line argument has the highest priority. However, you can set one key in file and other in env vars or command line args. Those will be merged.

Config File 📝

ConfReader will use config name property to search for a config file with that name.


By default, config reader will search for a config file in home or in current directory. You can override this behavior by using NewConfReader("myconf").WithSearchDirs("/etc/conf") of config builder

Referring fields

Field names are converted from camel case starting with lower case letter. For example if it code you refer to value as DB.DbName then it will be converted to

   dbName: "mydb"

Config file type could be any type supported by viper: JSON, TOML, YAML, HCL, INI, envfile and Java Properties files.

Environment Variables 📦

To set a flag via environment variable, make all letters uppercase and replace '.' with '_' in path. For example: app.Server.Port -> APP_SERVER_PORT

You can set a prefix for environment variables. For example NewConfReader("myconf").WithPrefix("MYAPP") will search for environment variables like MYAPP_DB_HOST

Command Line Arguments 💻

To set a configuration field via command line argument you need to pass and argument prefixes wiht -- and lowercase field name with path. Like Boolean value could be set by passing only flag name like --verbose

You can override name for a flag by using tag flag:"name" on a field. For example:

type Config struct {		
	DebugMode             bool `flag:"debug"`

You can set the flag by calling myapp --debug

Validations 🔞

You can validate fields of you configuration struct by using validate tag. For example:

type Config struct {		
    Host           string `validate:"required"`

For full list of validation tag refer to validator documentation.


  • How to set values for slice? If we have struct like
    type SliceConf struct {
        Slice []string
    then we can set values for slice in the following ways:
    • environment variable export SLICE="a,b"
    • command line argument myapp --slice", "a", "--slice", "b"
    • config file slice: [ "a", "b"]

Contributing 👏

We love help! Contribute by forking the repo and opening a pull requests or by creating an issue.

Credits ⭐

This package is based Viper Special thanks:

  • enviper for making environment variables work with viper
  • defaults for making default values work with structures




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type ConfReader

type ConfReader struct {
	// contains filtered or unexported fields
ConfReader reads configuration from config file, environment variables or command line flags.
Flags have precedence over env vars and env vars have precedence over config file.

For example:

	type NestedConf struct {
		Foo string

  	type Config struct{
      Nested NestedConf

in that case flag will be mapped automatically This flag could be also set by NESTED_FOO env var or by creating config file .ukama.yaml: nested:

foo: bar

func NewConfReader

func NewConfReader(configName string) *ConfReader

NewConfReader creates new instance of ConfReader configName is a name of config file name without extension and evn vars prefix

func (*ConfReader) Read

func (c *ConfReader) Read(configStruct interface{}) error

Read reads config from config file, env vars or flags.

func (*ConfReader) WithPrefix added in v0.0.5

func (c *ConfReader) WithPrefix(prefix string) *ConfReader

WithPrefix sets the prefix for environment variables

func (*ConfReader) WithSearchDirs

func (c *ConfReader) WithSearchDirs(s ...string) *ConfReader

Source Files


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