Isn't it awesome how Apache Commons CLI and the dozens of other Java command line parsers 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.java helps you create most beautiful command-line interfaces easily:

import java.util.Map;

import org.docopt.Docopt;

public final class NavalFate {

private static final String doc =
    "Naval Fate.\n"
    + "\n"
    + "Usage:\n"
    + "  naval_fate ship new <name>...\n"
    + "  naval_fate ship <name> move <x> <y> [--speed=<kn>]\n"
    + "  naval_fate ship shoot <x> <y>\n"
    + "  naval_fate mine (set|remove) <x> <y> [--moored | --drifting]\n"
    + "  naval_fate (-h | --help)\n"
    + "  naval_fate --version\n"
    + "\n"
    + "Options:\n"
    + "  -h --help     Show this screen.\n"
    + "  --version     Show version.\n"
    + "  --speed=<kn>  Speed in knots [default: 10].\n"
    + "  --moored      Moored (anchored) mine.\n"
    + "  --drifting    Drifting mine.\n"
    + "\n";

    public static void main(String[] args) {
      Map<String, Object> opts =
        new Docopt(doc).withVersion("Naval Fate 2.0").parse(args);
      System.out.println(opts);
    }
}

• Because Java does not support optional or named arguments, this port uses the Builder pattern to configure the parser instead of a simple method call.
• Because Java does not provide a way (native) way to read a class's Javadoc, there is no idiomatic way to supply the doc or version arguments. This implementation provides convenience methods to read these values from streams (e.g. files within the JAR) in addition to accepting String arguments.
• Because Java does not provide a way to get command line arguments other than in a main method, the argv parameter is required.
• Exiting the application when parsing arguments has been made optional. See the withExit method.

You can build a JAR using Maven http://maven.apache.org/ and include it as a dependency in your project. docopt.java is not currently available from Maven central.

Alternatevely, you can just copy the org.docopt package into your project--it is self-contained.

docopt.java is tested with Java 6 and Java 7.

import org.docopt.Docopt;

public Docopt(String doc)

Docopt takes one required argument:

• 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:

static final String doc =
    "Usage: my_program [-hso FILE] [--quiet | --verbose] [INPUT ...]\n"
    + "\n"
    + "-h --help    show this\n"
    + "-s --sorted  sorted output\n"
    + "-o FILE      specify output file [default: ./test.txt]\n"
    + "--quiet      print less text\n"
    + "--verbose    print more text\n"
    + "\n";

public Docopt(String doc)
public Docopt(InputStream doc)
public Docopt(InputStream doc, Charset charset)

Constructs an option parser from the doc argument or throws a DocoptLanguageError if it is malformed. If doc is an InputStream, the stream is read using the specified CharSet (UTF-8 by default).

public Map<String, Object> parse(List<String> argv)
public Map<String, Object> parse(String... argv)

parse takes one required argument:

• argv is an argument vector. The vector may be given as a List or as an array of Strings. Note that calling this method with no argument is equivalent to a giving an empty array!

The return value is a Map 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.py ship Guardian move 100 150 --speed=15

the return Map will be:

{--version=false,     remove=false,
 --speed=15,          ship=true,
 <name>=[Guardian],   set=false,
 <y>=150,             <x>=100,
 --moored=false,      new=false,
 --drifting=false,    shoot=false,
 mine=false,          --help=false,
 move=true}

public Docopt withHelp(boolean help)

withHelp takes one required argument:

• 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), invoke withHelp(false).

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

public Docopt withVersion(String version)

• version, by default null, 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.

  Note, when docopt is set to automatically handle the --version option, you still need to mention it in usage pattern for this to work. Also, for your users to know about them.

public Docopt withOptionsFirst(boolean optionsFirst)

• 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 the look like options. This can be used for strict compatibility with POSIX, or if you want to dispatch your arguments to other programs.

public Docopt withExit(boolean exit)

• exit, by default true. If set to false will cause parse to throw a DocoptExit exception instead of terminating the application.

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

static final 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:

static final String USAGE = 
    "Usage: my_program FILE\n" +
    "       my_program COUNT FILE";

Each pattern can consist of the following elements:

• <arguments>, 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 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 <angular-brackets> 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 <file>, --input <file>   # 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=<arg> --repeatable=<arg>]
                       [--another-repeatable=<arg>]...
                       [--not-repeatable=<arg>]
  
  # will be ['./here', './there']
  --repeatable=<arg>          [default: ./here ./there]
  
  # will be ['./here']
  --another-repeatable=<arg>  [default: ./here]
  
  # will be './here ./there', because it is not repeatable
  --not-repeatable=<arg>      [default: ./here ./there]

docopt.java follows semantic versioning.

• 0.6.0 Initial port based on version 0.6.1 of the reference implementation. All language agnostic tests pass.