Simple configuration reader for Go that handles a JSON settings file, along with command line flags and env vars, at the same time.

go get github.com/stephenb/simpleconfig

Given the following Go program,

package main

import (
	"fmt"
	"github.com/stephenb/simpleconfig"
)

func main() {
	// 1. Setup a map of supported options and their descriptions.
	opts := map[string]string {
		"setting1": "Setting one description.",
		"setting2": "Setting two description.",
	}

	// 2. Create a new config instance.
	config := simpleconfig.NewConfig(opts)
	config.JsonPath = "sample.json" // Could also use "config-path" CLI flag

	// 3. Parse the options from both the JSON settings file and CLI flags.
	err := config.Parse()
	if err != nil {
		panic(err.Error())
	}

	// 4. Config values are accessible via a normal map.
	fmt.Println("Config Map: ", config.Map)
}

and sample.json containing,

{
	"setting1": "Hello",
	"setting2": "World"
}

running the program will yield the following output:

With no CLI fags:

Config Map: map[setting1:Hello setting2:World]

With "-setting2=Josh" specified in the CLI flags:

Config Map: map[setting1:Hello setting2:Josh]

Once the Config is parsed, config.Map can be used just like a normal Go map. Note that the Config.Map has type "map[string]interface{}", which means you will need to use type assertion when using setting values.

Also, a basic usage explanation will be shown if you pass the "-h" CLI flag. This can be customized by re-implementing the Config's Usage function, similar to how you would customize the same Usage output in Go's own flag package.

Now ENV vars are also read into the configuration. The order of precedence is:

1. CLI Flags, 2. ENV Vars, 3. JSON Settings.

• Path to JSON config file can also be specified via "config-path" command-line flag
• CLI args will only be parsed into strings
• Default values aren't supported