popt

Package popt defines a series of helpers to define options for pflag and viper in one place.

Option usage

Use Option to define configuration options for your program. This allows quick and consistent bindings for configuration file options, flags and environment variables.

Start by configuring an option for your program.

var nameOption = popts.Option{
	Name:    "name",
	Default: "World",
	Usage:   "the name of the person you wish to greet",
	Env:     "HELLO_NAME",
	Flag:    "name",
	Short:   "n",
}

At init time, add the option to your program.

func init() {
	// Add name option
	if err := popt.AddOption(nameOption, pflag.CommandLine); err != nil {
		panic(err)
	}
}

When running your executable, bind your option and parse the flags.

func main() {
	// Bind env var and flag to viper
	popt.BindOption(nameOption, pflag.CommandLine)
	// Parse command-line flags
	pflag.Parse()
	// Read configuration file
	viper.SetConfigName("hello")
	viper.AddConfigPath(".")
	viper.SetConfigType("yaml")
	viper.ReadInConfig()
	fmt.Println("Hello", viper.GetString(nameOption.Name))
}

Example usage:

$ ./hello
Hello World

$ ./hello -h
Usage of ./hello:
  -n, --name string   the name of the person you wish to greet (default "World")
pflag: help requested

$ ./hello --name="Steve"
Hello Steve

$ HELLO_NAME="Brooklyn" ./hello
Hello Brooklyn

$ HELLO_NAME="Brooklyn" ./hello --name="Steve"
Hello Steve

$ echo 'name: "Sunshine"' > hello.yaml
$ ./hello
Hello Sunshine

You can also define your configuration options in a JSON file, to be loaded at runtime.

options.json

[
    {
        "name": "address",
        "default": "localhost",
        "usage": "The address of the remote host",
        "flag": "address",
        "short": "a",
        "env": "HELLO_ADDRESS"
    },
    {
        "name": "port",
        "default": 8080,
        "usage": "The port of the remote host",
        "flag": "port",
        "short": "p",
        "env": "HELLO_PORT"
    },
    {
        "default": false,
        "usage": "Make the operation more talkative",
        "flag": "verbose",
        "short": "v"
    }
]

Main

func main() {
	// error handling omitted for brevity
	f, err := os.Open("options.json")
	data, err := ioutil.ReadAll(f)
	var opts []popt.Option
	err = json.Unmarshal(data, &opts)
	err = popt.AddAndBindOptions(opts, pflag.CommandLine)
	pflag.Parse()
}

Usage

$ ./popt_json -h
Usage of ./popt_json:
-a, --address string   The address of the remote host (default "localhost")
-p, --port string      The port of the remote host (default "8080")
-v, --verbose          Make the operation more talkative
pflag: help requested

CAVEAT: Beware that your options defined in JSON will follow JSON typing; in particular, all your numbers will be float64s.

License

Original work, Copyright 2017 Pantomath SAS
Modified work, Copyright (c) 2019 Charles Francoise

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.