Go: Implementing Subcommands With go-flags

github.com/jessevdk/go-flags is the go-to tool for argument processing. It supports subcommands but understanding how to do it is a feat of reverse-engineering. So, here is an example.


package main

import (


type readParameters struct {

type writeParameters struct {

type parameters struct {
    Verbose bool `short:"v" long:"verbose" description:"Display logging"`
    Read readParameters `command:"read" alias:"r" description:"Read functions"`
    Write readParameters `command:"write" alias:"w" description:"Write functions"`

var (
    arguments = new(parameters)

func main() {
    p := flags.NewParser(arguments, flags.Default)

    _, err := p.Parse()
    if err != nil {

    switch p.Active.Name {
    case "read":
    case "write":

If you were to save it as "args.go", this is what the help and the usage would look like:

$ go run args.go -h
  args [OPTIONS] 

Application Options:
  -v, --verbose  Display logging

Help Options:
  -h, --help     Show this help message

Available commands:
  read   Read functions (aliases: r)
  write  Write functions (aliases: w)

exit status 255

$ go run args.go read 

Best Argument-Processing for .NET/C#

After trying NDesk.Options and Fluent, I am nothing but impressed with CLAP (“Command-Line Auto-Parser”). It completely relies on reflection and parameter attributes (usually just one or two) to automatically marshal your values, assign defaults, enforce requiredness, and provide command-line documentation. It’s beautiful and, so far, flawless. Well done.

using CLAP;

namespace MyNamespace
    class Program
        [Verb(IsDefault = true, Description = "Print the current version of the given package and, optionally, increment it.")]
        public void Version(
            [Description("Project path")]
            string projectPath,

            [Description("Package name")]
            string packageName,

            [Description("Base version to increment from (if lower than current, else use current)")]
            string baseVersion = null,

            [Description("Increment the version before returning")]
            bool increment = false
            // ...

If you don’t decorate with the “Required” attribute and don’t provide a default value the parameter will default to null. I explicitly set baseVersion to a default of null because I prefer being explicit.