Programming language: C#
License: MIT License
Tags: Parsing     Library     Parser     Command     Line     Argument     Option     Syntax     Shell    
Latest version: v2.9.0-preview1

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Command Line Parser Library for CLR and NetStandard

Note: the API surface has changed since v1.9.x and earlier. If you are looking for documentation on v1.9.x, please see stable-

The Command Line Parser Library offers CLR applications a clean and concise API for manipulating command line arguments and related tasks, such as defining switches, options and verb commands. It allows you to display a help screen with a high degree of customization and a simple way to report syntax errors to the end user.

C:\Project> NuGet Install CommandLineParser

Nightly Build

Nightly version of the CommandLineParser can be downloaded from github Releases.

The Last new features and fixes, read changelog

NOTE: Mentioned F# Support is provided via CommandLineParser.FSharp package with FSharp dependencies.

This library provides hassle free command line parsing with a constantly updated API since 2005.

At a glance:

  • Compatible with .NET Framework 4.0+, Mono 2.1+ Profile, .NET Standard and .NET Core
  • Doesn't depend on other packages (No dependencies beyond standard base libraries)
  • One line parsing using default singleton: CommandLine.Parser.Default.ParseArguments(...) and three overload methods.
  • Automatic or one line help screen generator: HelpText.AutoBuild(...).
  • Supports --help, --version, version and help [verb] by default with customization.
  • Map to sequences (via IEnumerable<T> and similar) and scalar types, including Enums and Nullable<T>.
  • You can also map to every type with a constructor that accepts a string (like System.Uri) for reference and value types.
  • Verbs can be array of types collected from Plugins or IoC container.
  • Define verb commands similar to git commit -a.
  • Support default verb.
  • Support Mutable and Immutable types.
  • Support HelpText localization.
  • Support ordering of options in HelpText.
  • Support Mutually Exclusive Options and Option groups.
  • Support named and value options.
  • Support Asynchronous programming with async and await.
  • Unparsing support: CommandLine.Parser.Default.FormatCommandLine<T>(T options).
  • CommandLineParser.FSharp package is F#-friendly with support for option<'a>, see demo. NOTE: This is a separate NuGet package.
  • Include wiki documentation with lot of examples ready to run online.
  • Support Source Link and symbolic nuget package snupkg.
  • Tested in Windows, Linux Ubuntu 18.04 and Mac OS.
  • Most of features applies with a CoC philosophy.
  • C# demo: source here.

Getting Started with the Command Line Parser Library

You can utilize the parser library in several ways:

Quick Start Examples

  1. Create a class to define valid options, and to receive the parsed options.
  2. Call ParseArguments with the args string array.

C# Quick Start:

using System;
using CommandLine;

namespace QuickStart
    class Program
        public class Options
            [Option('v', "verbose", Required = false, HelpText = "Set output to verbose messages.")]
            public bool Verbose { get; set; }

        static void Main(string[] args)
                   .WithParsed<Options>(o =>
                       if (o.Verbose)
                           Console.WriteLine($"Verbose output enabled. Current Arguments: -v {o.Verbose}");
                           Console.WriteLine("Quick Start Example! App is in Verbose mode!");
                           Console.WriteLine($"Current Arguments: -v {o.Verbose}");
                           Console.WriteLine("Quick Start Example!");

C# Examples:

Click to expand!

class Options
  [Option('r', "read", Required = true, HelpText = "Input files to be processed.")]
  public IEnumerable<string> InputFiles { get; set; }

  // Omitting long name, defaults to name of property, ie "--verbose"
    Default = false,
    HelpText = "Prints all messages to standard output.")]
  public bool Verbose { get; set; }

    Default = false,
    HelpText = "Read from stdin")]
  public bool stdin { get; set; }

  [Value(0, MetaName = "offset", HelpText = "File offset.")]
  public long? Offset { get; set; }

static void Main(string[] args)
static void RunOptions(Options opts)
  //handle options
static void HandleParseError(IEnumerable<Error> errs)
  //handle errors

Demo to show IEnumerable options and other usage: Online Demo

F# Examples:

Click to expand!

type options = {
  [<Option('r', "read", Required = true, HelpText = "Input files.")>] files : seq<string>;
  [<Option(HelpText = "Prints all messages to standard output.")>] verbose : bool;
  [<Option(Default = "русский", HelpText = "Content language.")>] language : string;
  [<Value(0, MetaName="offset", HelpText = "File offset.")>] offset : int64 option;

let main argv =
  let result = CommandLine.Parser.Default.ParseArguments<options>(argv)
  match result with
  | :? Parsed<options> as parsed -> run parsed.Value
  | :? NotParsed<options> as notParsed -> fail notParsed.Errors

VB.NET Example:

Click to expand!

Class Options
    <CommandLine.Option('r', "read", Required := true,
    HelpText:="Input files to be processed.")>
    Public Property InputFiles As IEnumerable(Of String)

    ' Omitting long name, defaults to name of property, ie "--verbose"
    HelpText:="Prints all messages to standard output.")>
    Public Property Verbose As Boolean

    HelpText:="Content language.")>
    Public Property Language As String

    <CommandLine.Value(0, MetaName:="offset",
    HelpText:="File offset.")>
    Public Property Offset As Long?
End Class

Sub Main(ByVal args As String())
    CommandLine.Parser.Default.ParseArguments(Of Options)(args) _
        .WithParsed(Function(opts As Options) RunOptionsAndReturnExitCode(opts)) _
        .WithNotParsed(Function(errs As IEnumerable(Of [Error])) 1)
End Sub

For verbs:

  1. Create separate option classes for each verb. An options base class is supported.
  2. Call ParseArguments with all the verb attribute decorated options classes.
  3. Use MapResult to direct program flow to the verb that was parsed.

C# example:

Click to expand!

[Verb("add", HelpText = "Add file contents to the index.")]
class AddOptions {
  //normal options here
[Verb("commit", HelpText = "Record changes to the repository.")]
class CommitOptions {
  //commit options here
[Verb("clone", HelpText = "Clone a repository into a new directory.")]
class CloneOptions {
  //clone options here

int Main(string[] args) {
  return CommandLine.Parser.Default.ParseArguments<AddOptions, CommitOptions, CloneOptions>(args)
      (AddOptions opts) => RunAddAndReturnExitCode(opts),
      (CommitOptions opts) => RunCommitAndReturnExitCode(opts),
      (CloneOptions opts) => RunCloneAndReturnExitCode(opts),
      errs => 1);

VB.NET example:

Click to expand!

<CommandLine.Verb("add", HelpText:="Add file contents to the index.")>
Public Class AddOptions
    'Normal options here
End Class
<CommandLine.Verb("commit", HelpText:="Record changes to the repository.")>
Public Class CommitOptions
    'Normal options here
End Class
<CommandLine.Verb("clone", HelpText:="Clone a repository into a new directory.")>
Public Class CloneOptions
    'Normal options here
End Class

Function Main(ByVal args As String()) As Integer
    Return CommandLine.Parser.Default.ParseArguments(Of AddOptions, CommitOptions, CloneOptions)(args) _
              (Function(opts As AddOptions) RunAddAndReturnExitCode(opts)),
              (Function(opts As CommitOptions) RunCommitAndReturnExitCode(opts)),
              (Function(opts As CloneOptions) RunCloneAndReturnExitCode(opts)),
              (Function(errs As IEnumerable(Of [Error])) 1)
End Function

F# Example:

Click to expand!

open CommandLine

[<Verb("add", HelpText = "Add file contents to the index.")>]
type AddOptions = {
  // normal options here
[<Verb("commit", HelpText = "Record changes to the repository.")>]
type CommitOptions = {
  // normal options here
[<Verb("clone", HelpText = "Clone a repository into a new directory.")>]
type CloneOptions = {
  // normal options here

let main args =
  let result = Parser.Default.ParseArguments<AddOptions, CommitOptions, CloneOptions> args
  match result with
  | :? CommandLine.Parsed<obj> as command ->
    match command.Value with
    | :? AddOptions as opts -> RunAddAndReturnExitCode opts
    | :? CommitOptions as opts -> RunCommitAndReturnExitCode opts
    | :? CloneOptions as opts -> RunCloneAndReturnExitCode opts
  | :? CommandLine.NotParsed<obj> -> 1

Release History

See the [changelog](CHANGELOG.md)


First off, Thank you! All contributions are welcome.

Please consider sticking with the GNU getopt standard for command line parsing.

Additionally, for easiest diff compares, please follow the project's tabs settings. Utilizing the EditorConfig extension for Visual Studio/your favorite IDE is recommended.

And most importantly, please target the develop branch in your pull requests!

Main Contributors (alphabetical order):

  • Alexander Fast (@mizipzor)
  • Dan Nemec (@nemec)
  • Eric Newton (@ericnewton76)
  • Kevin Moore (@gimmemoore)
  • Moh-Hassan (@moh-hassan)
  • Steven Evans
  • Thomas Démoulins (@Thilas)

Resources for newcomers:


  • Giacomo Stelluti Scala
    • gsscoder AT gmail DOT com (use this for everything that is not available via GitHub features)
    • GitHub: gsscoder
    • Blog
    • Twitter
  • Dan Nemec
  • Eric Newton
  • Moh-Hassan