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Port of docopt to .net

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docopt.net is a .NET port of docopt

Isn't it awesome how CommandLineParser <https://nuget.org/packages/CommandLineParser/>_ and PowerArgs <https://nuget.org/packages/PowerArgs/>_ generate help messages based on your code?!

Hell no! You know what's awesome? It's when the option parser is generated based on the beautiful help message that you write yourself! This way you don't need to write this stupid repeatable parser-code, and instead can write only the help message--the way you want it.

docopt.net helps you create most beautiful command-line interfaces easily:

.. code:: c#

using System; using DocoptNet;

namespace NavalFate { internal class Program { private const string usage = @"Naval Fate.

    naval_fate.exe ship new <name>...
    naval_fate.exe ship <name> move <x> <y> [--speed=<kn>]
    naval_fate.exe ship shoot <x> <y>
    naval_fate.exe mine (set|remove) <x> <y> [--moored | --drifting]
    naval_fate.exe (-h | --help)
    naval_fate.exe --version

    -h --help     Show this screen.
    --version     Show version.
    --speed=<kn>  Speed in knots [default: 10].
    --moored      Moored (anchored) mine.
    --drifting    Drifting mine.


      private static void Main(string[] args)
          var arguments = new Docopt().Apply(usage, args, version: "Naval Fate 2.0", exit: true);
          foreach (var argument in arguments)
              Console.WriteLine("{0} = {1}", argument.Key, argument.Value);


Beat that! The option parser is generated based on the docstring above that is passed to the Docopt.Apply method. Docopt.Apply parses the usage pattern ("Usage: ...") and option descriptions (lines starting with dash ``-``) and ensures that the program invocation matches the usage pattern; it parses options, arguments and commands based on that. The basic idea is that a good help message has all necessary information in it to make a parser.

Differences from reference python implementation

  • This port should be fully Docopt language compatible with the python reference implementation.

  • Because C# is statically typed, the return dictionary is of type IDictionary<string,ValueObject> where ValueObject is a simple wrapper class around entry values.


Use nuget

nuget install Docopt.net -Version

Alternatively, you can just drop DocoptNet.dll file into your project--it is self-contained.

docopt.net is tested with Visual Studio 2012.


.. code:: c#

using DocoptNet;

.. code:: c#

public IDictionary Apply(string doc, string cmdLine, bool help = true, object version = null, bool optionsFirst = false, bool exit = false)

public IDictionary Apply(string doc, ICollection argv, bool help = true, object version = null, bool optionsFirst = false, bool exit = false)

Apply takes 1 required and 5 optional arguments:

  • doc is a string that contains a help message that will be parsed to create the option parser. The simple rules of how to write such a help message are given in next sections. Here is a quick example of such a string:

.. code:: c#

const string USAGE = 
@"Usage: my_program [-hso FILE] [--quiet | --verbose] [INPUT ...]

-h --help    show this
-s --sorted  sorted output
-o FILE      specify output file [default: ./test.txt]
--quiet      print less text
--verbose    print more text

  • argv is an optional argument vector; Alternatively you can supply a command line string cmdLine.

  • help, by default true, specifies whether the parser should automatically print the help message (supplied as doc) and terminate, in case -h or --help option is encountered (options should exist in usage pattern, more on that below). If you want to handle -h or --help options manually (as other options), set help: false.

    Note, you can override the print and exit behaviour by providing a custom handler for the Docopt.PrintExit event. e.g.

.. code:: c#

var docopt = new Docopt();
docopt.PrintExit += MyCustomPrintExit;
  • version, by default null, is an optional argument that specifies the version of your program. If supplied, then, (assuming --version option is mentioned in usage pattern) when parser encounters the --version option, it will print the supplied version and terminate. version could be any printable object, but most likely a string, e.g. "2.1.0rc1".

    Note, when docopt.net is set to automatically handle -h, --help and --version options, you still need to mention them in usage pattern for this to work. Also, for your users to know about them.

  • optionsFirst, by default false. If set to true will disallow mixing options and positional argument. I.e. after first positional argument, all arguments will be interpreted as positional even if they look like options. This can be used for strict compatibility with POSIX, or if you want to dispatch your arguments to other programs.

  • exit, by default false. If set to false will raise exceptions based on DocoptBaseException and will not print or exit. If set to true any occurence of DocoptBaseException will be caught by Docopt.Apply(), the error message or the usage will be printed, and the program will exit with error code 0 if it's a DocoptExitException, 1 otherwise.

The return value is a simple dictionary with options, arguments and commands as keys, spelled exactly like in your help message. Long versions of options are given priority. For example, if you invoke the top example as::

naval_fate ship Guardian move 100 150 --speed=15

the return dictionary will be:

.. code:: python

{'--drifting': False,    'mine': False,
 '--help': False,        'move': True,
 '--moored': False,      'new': False,
 '--speed': '15',        'remove': False,
 '--version': False,     'set': False,
 '<name>': ['Guardian'], 'ship': True,
 '<x>': '100',           'shoot': False,
 '<y>': '150'}

Help message format

Help message consists of 2 parts:

  • Usage pattern, e.g.::

    Usage: my_program [-hso FILE] [--quiet | --verbose] [INPUT ...]

  • Option descriptions, e.g.::

    -h --help show this -s --sorted sorted output -o FILE specify output file [default: ./test.txt] --quiet print less text --verbose print more text

Their format is described below; other text is ignored.

Usage pattern format

Usage pattern is a substring of doc that starts with usage: (case insensitive) and ends with a visibly empty line. Minimum example:

.. code:: c#

const string USAGE = "Usage: my_program";

The first word after usage: is interpreted as your program's name. You can specify your program's name several times to signify several exclusive patterns:

.. code:: c#

const string USAGE = 
@"Usage: my_program FILE
         my_program COUNT FILE";

Each pattern can consist of the following elements:

  • , ARGUMENTS. Arguments are specified as either upper-case words, e.g. my_program CONTENT-PATH or words surrounded by angular brackets: my_program <content-path>.
  • --options. Options are words started with dash (-), e.g. --output, -o. You can stack several of one-letter options, e.g. -oiv which will be the same as -o -i -v. The options can have arguments, e.g. --input=FILE or -i FILE or even -iFILE. However it is important that you specify option descriptions if you want your option to have an argument, a default value, or specify synonymous short/long versions of the option (see next section on option descriptions).
  • commands are words that do not follow the described above conventions of --options or <arguments> or ARGUMENTS, plus two special commands: dash ``-`` and double dash ``--`` (see below).

Use the following constructs to specify patterns:

  • [ ] (brackets) optional elements. e.g.: my_program [-hvqo FILE]
  • ( ) (parens) required elements. All elements that are not put in [ ] are also required, e.g.: my_program --path=<path> <file>... is the same as my_program (--path=<path> <file>...). (Note, required options might be not a good idea for your users).
  • | (pipe) mutually exclusive elements. Group them using ( ) if one of the mutually exclusive elements is required: my_program (--clockwise | --counter-clockwise) TIME. Group them using [ ] if none of the mutually-exclusive elements are required: my_program [--left | --right].
  • ... (ellipsis) one or more elements. To specify that arbitrary number of repeating elements could be accepted, use ellipsis (...), e.g. my_program FILE ... means one or more FILE-s are accepted. If you want to accept zero or more elements, use brackets, e.g.: my_program [FILE ...]. Ellipsis works as a unary operator on the expression to the left.
  • [options] (case sensitive) shortcut for any options. You can use it if you want to specify that the usage pattern could be provided with any options defined below in the option-descriptions and do not want to enumerate them all in usage-pattern.
  • ``[--]``. Double dash ``--`` is used by convention to separate positional arguments that can be mistaken for options. In order to support this convention add ``[--]`` to your usage patterns.
  • ``[-]``. Single dash ``-`` is used by convention to signify that stdin is used instead of a file. To support this add ``[-]`` to your usage patterns. ``-`` acts as a normal command.

If your pattern allows to match argument-less option (a flag) several times::

Usage: my_program [-v | -vv | -vvv]

then number of occurrences of the option will be counted. I.e. args['-v'] will be 2 if program was invoked as my_program -vv. Same works for commands.

If your usage patterns allows to match same-named option with argument or positional argument several times, the matched arguments will be collected into a list::

Usage: my_program <file> <file> --path=<path>...

I.e. invoked with my_program file1 file2 --path=./here --path=./there the returned dict will contain args['<file>'] == ['file1', 'file2'] and args['--path'] == ['./here', './there'].

Option descriptions format

Option descriptions consist of a list of options that you put below your usage patterns.

It is necessary to list option descriptions in order to specify:

  • synonymous short and long options,
  • if an option has an argument,
  • if option's argument has a default value.

The rules are as follows:

  • Every line in doc that starts with - or -- (not counting spaces) is treated as an option description, e.g.::

    Options: --verbose # GOOD -o FILE # GOOD Other: --bad # BAD, line does not start with dash -

  • To specify that option has an argument, put a word describing that argument after space (or equals ``=`` sign) as shown below. Follow either or UPPER-CASE convention for options' arguments. You can use comma if you want to separate options. In the example below, both lines are valid, however you are recommended to stick to a single style.::

    -o FILE --output=FILE # without comma, with = sign -i , --input # with comma, without = sing

  • Use two spaces to separate options with their informal description::

    --verbose More text. # BAD, will be treated as if verbose option had # an argument More, so use 2 spaces instead -q Quit. # GOOD -o FILE Output file. # GOOD --stdout Use stdout. # GOOD, 2 spaces

  • If you want to set a default value for an option with an argument, put it into the option-description, in form [default: <my-default-value>]::

    --coefficient=K The K coefficient [default: 2.95] --output=FILE Output file [default: test.txt] --directory=DIR Some directory [default: ./]

  • If the option is not repeatable, the value inside [default: ...] will be interpreted as string. If it is repeatable, it will be splited into a list on whitespace::

    Usage: my_program [--repeatable= --repeatable=] [--another-repeatable=]... [--not-repeatable=]

    will be ['./here', './there']

    --repeatable= [default: ./here ./there]

    will be ['./here']

    --another-repeatable= [default: ./here]

    will be './here ./there', because it is not repeatable

    --not-repeatable= [default: ./here ./there]

Strongly typed arguments with T4 Macro

Include the T4DocoptNet.tt* files in your main project to enable the strongly type arguments code generation. Then add a file called Main.usage.txt to your project. Store the usage document in this file instead of creating a string constant in your program. When the T4DocoptNet.tt macro is applied, a class called MainArgs in a file called T4DocoptNet.cs will be generated. It will publish the following members:

  • USAGE public string constant that returns the usage document.

  • A set of properties that correspond to the commands, arguments, switches and options defined in the usage document.

Note that if you name the usage file Foo.usage.txt, the generated class will be called FooArgs.

Sample Main.usage.txt


Usage: prog command ARG FILES... [-o --switch --long=ARG]

Resulting T4DocopNet.cs

The generated class publishes the different argument items as strongly typed properties. Its constructor accepts the same parameters than the Docopt.Apply method. The original usage text is published as a string constant e.g. MainArgs.USAGE.

.. code:: c#

// Generated class for Main.usage.txt public class MainArgs { public const string USAGE = @"Test.

Usage: prog command ARG FILES... [-o --switch --long=ARG] "; private readonly IDictionary _args; public MainArgs(ICollection argv, bool help = true, object version = null, bool optionsFirst = false, bool exit = false) { _args = new Docopt().Apply(USAGE, argv, help, version, optionsFirst, exit); }

public IDictionary<string, ValueObject> Args
  get { return _args; }

public bool CmdCommand { get { return _args["command"].IsTrue; } }
public string ArgArg { get { return _args["ARG"].ToString(); } }
public bool OptO { get { return _args["-o"].IsTrue; } }
public string OptLong { get { return _args["--long"].ToString(); } }
public bool OptSwitch { get { return _args["--switch"].IsTrue; } }
public ArrayList ArgFiles { get { return _args["FILES"].AsList; } }


Using the generated code

.. code:: c#

class Program {

 static void DoStuff(string arg, bool flagO, string longValue)
 // ...

static void Main(string[] argv)
  // Automatically exit(1) if invalid arguments
  var args = new MainArgs(argv, exit: true);
  if (args.CmdCommand)
    Console.WriteLine("First command");
    DoStuff(args.ArgArg, args.OptO, args.OptLong);


You can also access the MainArgs.USAGE string constant as follows: .. code:: c#

Console.WriteLine(Usage: + MainArgs.USAGE)

Getting rid of the T4 macro

If you don't want to use the strongly typed arguments, just delete the T4DocoptNet.* files from the project.


docopt.net follows semantic versioning <http://semver.org>_. The first release with stable API will be 1.0.0 (soon). Until then, you are encouraged to specify explicitly the version in your dependency tools, e.g.::

nuget install docopt.net -Version
  • Added support for .net core RC2.
  • Double creation of property bug fix. T4DocoptNet.tt assembly path fix.
  • Added strongly typed arguments through T4 macro. ValueObject interface cleanup. exit:true parameter behavior fix.
  • Clarified exit parameter behaviour.
  • Added exit parameter.
  • Fixed docopt capitalisation.
  • Initial port. All reference language agnostic tests pass.
docopt.net open issues Ask a question     (View All Issues)
  • about 6 years create a nuget package for a single Docopt.cs file
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