NAME
    OptArgs2 - command-line argument and option processor

VERSION
    0.0.6 (2016-07-03)

SYNOPSIS
        #!/usr/bin/env perl
        use OptArgs2;

        arg item => (
            isa      => 'Str',
            required => 1,
            comment  => 'the item to paint',
        );

        opt quiet => (
            isa     => 'Flag',
            alias   => 'q',
            comment => 'output nothing while working',
        );

        my $ref = optargs;

        print "Painting $ref->{item}\n" unless $ref->{quiet};

DESCRIPTION
    OptArgs2 processes command line arguments, options, and subcommands
    according to the following definitions:

    Command
        A program run from the command line to perform a task.

    Arguments
        Arguments are positional parameters that pass information to a
        command. Arguments can be optional, but they should not be confused
        with Options below.

    Options
        Options are non-positional parameters that pass information to a
        command. They are generally not required to be present (hence the
        name Option) but that is configurable. All options have a long form
        prefixed by '--', and may have a single letter alias prefixed by
        '-'.

    Subcommands
        From the users point of view a subcommand is a special argument with
        its own set of arguments and options. However from a code authoring
        perspective subcommands are often implemented as stand-alone
        programs, called from the main script when the appropriate command
        arguments are given.

    OptArgs2 is a re-write of the original OptArgs module with a cleaner
    code base and improved API. It should be preferred over OptArgs for new
    projects however OptArgs is not likely to disappear from CPAN anytime
    soon. Users converting to OptArgs2 from OptArgs need to be aware of the
    following:

    Obvious API changes: cmd(), subcmd()
        Commands and subcommands must now be explicitly defined using
        "cmd()" and "subcmd()".

    class_optargs() no longer loads the class
        Users must specifically require the class if they want to use it
        afterwards:

            my ($class, $opts) = class_optargs('App::demo');
            eval "require $class" or die $@; # new requirement

    Bool options with no default display as "--[no-]bool"
        A Bool option without a default is now displayed with the "[no-]"
        prefix. What this means in practise is that many of your existing
        Bool options should likely become Flag options instead.

  Simple Commands
    To demonstrate the simple use case (i.e. with no subcommands) lets put
    the code from the synopsis in a file called "paint" and observe the
    following interactions from the shell:

        $ ./paint
        usage: paint ITEM [OPTIONS...]

          arguments:
            ITEM          the item to paint

          options:
            --quiet, -q   output nothing while working

    The "optargs()" function parses the command line according to the
    previous "opt()" and "arg()" declarations and returns a single HASH
    reference. If the command is not called correctly then an exception is
    thrown containing an automatically generated usage message as shown
    above. Because OptArgs2 fully knows the valid arguments and options it
    can detect a wide range of errors:

        $ ./paint wall message
        error: unexpected option or argument: red

    So let's add that missing argument definition:

        arg message => (
            isa      => 'Str',
            comment  => 'the message to paint on the item',
            greedy   => 1,
        );

    And then check the usage again:

        $ ./paint
        usage: paint ITEM [MESSAGE...] [OPTIONS...]

          arguments:
            ITEM          the item to paint
            MESSAGE       the message to paint on the item

          options:
            --quiet, -q   output nothing while working

    Note that optional arguments are surrounded by square brackets, and that
    three dots (...) are postfixed to greedy arguments. A greedy argument
    will swallow whatever is left on the comand line:

        $ ./paint wall Perl is great
        Painting on wall: "Perl is great".

    Note that it probably doesn't make sense to define any more arguments
    once you have a greedy argument. Let's imagine you now want the user to
    be able to choose the colour if they don't like the default. An option
    might make sense here:

        opt colour => (
            isa           => 'Str',
            default       => 'blue',
            show_default  => 1,
            comment       => 'the colour to use',
        );

    This now produces the following usage output:

        usage: paint ITEM [MESSAGE...] [OPTIONS...]

          arguments:
            ITEM               the item to paint
            MESSAGE            the message to paint on the item
 
          options:
            --colour=STR, -c   the colour to use [default: blue]
            --quiet,      -q   output nothing while working

    The command line is parsed first for arguments, then for options, in the
    same order in which they are defined. This probably only of interest if
    you are using trigger actions on your options (see FUNCTIONS below for
    details).

  Multi-Level Commands
    Commands with subcommands require a different coding model and syntax
    which we will describe over three phases:

    Definitions
        Your command structure is defined using calls to the "cmd()" and
        "subcmd()" functions. The first argument to both functions is the
        name of the Perl class that implements the (sub-)command.

            cmd 'App::demo' => (
                comment => 'the demo command',
                optargs => sub {
                    arg command => (
                        isa      => 'SubCmd',
                        required => 1,
                        comment  => 'command to run',
                    );

                    opt quiet => (
                        isa     => 'Flag',
                        alias   => 'q',
                        comment => 'run quietly',
                    );
                },
            );

            subcmd 'App::demo::foo' => (
                comment => 'demo foo',
                optargs => sub {
                    arg action => (
                        isa      => 'Str',
                        required => 1,
                        comment  => 'command to run',
                    );
                },
            );

            subcmd 'App::demo::bar' => (
                comment => 'demo bar',
                optargs => sub {
                    opt baz => (
                        isa => 'Counter',
                        comment => '+1',
                    );
                },
            );

            # Command hierarchy for the above code:
            # demo COMMAND [OPTIONS...]
            #     demo foo ACTION [OPTIONS...]
            #     demo bar [OPTIONS...]

        An argument of type 'SubCmd' indicates subcommands can occur in that
        position. The command hierarchy is based upon the natural
        parent/child structure of the class names. This definition can be
        done in your main script, or in one or more separate packages or
        plugins, as you like.

    Parsing
        The "class_optargs()" function is called instead of "optargs()" to
        parse the @ARGV array and call the appropriate "arg()" and "opt()"
        definitions as needed. It's first argument is generally the
        top-level command name you used in your first "cmd()" call.

            my ($class, $opts) = class_optargs('App::demo');

            printf "Running %s with %s\n", $class, Dumper($opts)
              unless $opts->{quiet};

        The additional return value $class is the name of the actual
        (sub-)command to which the $opts HASHref applies. Usage exceptions
        are raised just the same as with the "optargs()" function.

            error: unknown option "--invalid"

            usage: demo COMMAND [OPTIONS...]

                COMMAND       command to run
                  bar           demo bar
                  foo           demo foo

                --quiet, -q   run quietly

        Note that options are inherited by subcommands.

    Dispatch/Execution
        Once you have the subcommand name and the option/argument hashref
        you can either execute the action or dispatch to the appropriate
        class/package as you like.

        There are probably several ways to layout command classes when you
        have lots of subcommands. Here is one way that seems to work for
        this module's author.

        lib/App/demo.pm, lib/App/demo/subcmd.pm
            I typically put the actual (sub-)command implementations in
            lib/App/demo.pm and lib/App/demo/subcmd.pm. App::demo itself
            only needs to exists if the root command does something. However
            I tend to also make App::demo the base class for all subcommands
            so it is often a non-trivial piece of code.

        lib/App/demo/OptArgs.pm
            App::demo::OptArgs is where I put all of my command definitions
            with names that match the actual implementation modules.

                package App::demo::OptArgs;
                use OptArgs2;

                cmd 'App::demo' => (
                    comment => 'the demo app',
                    optargs => sub {
                        #...
                    },
                )

            The reason for keeping this separate from lib/App/demo.pm is
            speed of loading. I don't want to have to load all of the
            modules that App::demo itself uses just to find out that I
            called the command incorrectly.

        bin/demo
            The command script itself is then usually fairly short:

                #!/usr/bin/env perl
                use OptArgs2 'class_optargs';
                use App::demo::OptArgs;

                my ($class, $opts) = class_optargs('App::demo');
                eval "require $class" or die $@;
                $class->new->run($opts);

            The above does nothing more than load the definitions from
            App::demo::OptArgs, obtain the command name and options hashref,
            and then loads the appropriate package to run the command.

  Formatting of Usage Messages
    Usage messages attempt to present as much information as possible to the
    caller. Here is a brief overview of how the various types look and/or
    change depending on things like defaults.

    The presentation of Bool options in usage messages is as follows:

        Name        Type        Default         Presentation
        ----        ----        -------         ------------
        option      Bool        undef           --[no-]option
        option      Bool        true            --no-option
        option      Bool        false           --option
        option      Counter     *               --option

    The Flag option type is like a Bool that can only be set to true or left
    undefined. This makes sense for things such as "--help" or "--version"
    for which you never need to see a "--no" prefix.

        Name        Type        Default         Presentation
        ----        ----        -------         ------------
        option      Flag        always undef    --option

    Note that Flags also makes sense for "negative" options which will only
    ever turn things off:

        Name        Type        Default         Presentation
        ----        ----        -------         ------------
        no_option   Flag        always undef    --no-option

        # In Perl
        opt no_foo => (
            isa     => 'Flag',
            comment => 'disable the foo feature',
        );

        # Then later do { } unless $opts->{no_foo}

    The remaining types are presented as follows:

        Name        Type        isa_name        Presentation
        ----        ----        --------        ------------
        option      ArrayRef    -               --option=STR
        option      HashRef     -               --option=STR
        option      Int         -               --option=INT
        option      Num         -               --option=NUM
        option      Str         -               --option=STR
        option      *           XX              --option=XX

    Defaults TO BE COMPLETED.

FUNCTIONS
    The following functions are exported by default.

    arg( $name, %parameters )
        Define a command argument, for example:

            arg name => (
                comment  => 'the file to parse',
                default  => '-',
                greedy   => 0,
                isa      => 'Str',
                required => 1,
            );

        The "arg()" function accepts the following parameters:

        abbrev
            Valid for arguments of type 'SubCmd' only. When set to true then
            subcommands can be abbreviated, up to their shortest, unique
            values.

        comment
            Required. Used to generate the usage/help message.

        default
            The value set when the argument is not given. Conflicts with the
            'required' parameter.

            If this is a subroutine reference it will be called with a
            hashref containg all option/argument values after parsing the
            source has finished. The value to be set must be returned, and
            any changes to the hashref are ignored.

        greedy
            If true the argument swallows the rest of the command line.

        fallback
            A hashref containing an argument definition for the event that a
            subcommand match is not found. This parameter is only valid when
            "isa" is a "SubCmd". The hashref must contain "isa", "name" and
            "comment" key/value pairs, and may contain a "greedy" key/value
            pair.

            This is generally useful when you want to calculate a command
            alias from a configuration file at runtime, or otherwise run
            commands which don't easily fall into the OptArgs2 subcommand
            model.

        isa Required. Is mapped to a Getopt::Long type according to the
            following table:

                 optargs         Getopt::Long
                ------------------------------
                 'Str'           '=s'
                 'Int'           '=i'
                 'Num'           '=f'
                 'ArrayRef'      's@'
                 'HashRef'       's%'
                 'SubCmd'        '=s'

        required
            Set to a true value when the caller must specify this argument.
            Conflicts with the 'default' parameter.

        show_default
            If set to a true value then usage messages will show the default
            value.

    class_optargs( $class, [ @argv ] ) -> ($subclass, $opts)
        Parse @ARGV by default (or @argv when given) for the arguments and
        options defined for command $class. @ARGV will first be decoded into
        UTF-8 (if necessary) from whatever I18N::Langinfo says your current
        locale codeset is.

        Throws an error / usage exception object (typically
        "OptArgs2::Usage") for missing or invalid arguments/options.

        Returns the following two values:

        $subclass
            The actual subcommand name that was matched by parsing the
            arguments. This may be the same as $class.

        $opts
            a hashref containing key/value pairs for options and arguments
            *combined*.

        As an aid for testing, if the passed in argument @argv (not @ARGV)
        contains a HASH reference, the key/value combinations of the hash
        will be added as options. An undefined value means a boolean option.

    cmd( $class, %parameters ) -> OptArgs2::Cmd
        Define a top-level command identified by $class which is typically a
        Perl package name. The following parameters are accepted:

        comment
            A description of the command. Required.

        optargs
            A subref containing calls to "arg()" and "opt". Note that
            options are inherited by subcommands so you don't need to define
            them again in child subcommands.

    opt( $name, %parameters )
        Define a command option, for example:

            opt colour => (
                alias        => 'c',
                comment      => 'the colour to paint',
                default      => 'blue',
                show_default => 1,
                isa          => 'Str',
            );

        Any underscores in $name are be replaced by dashes (-) for
        presentation and command-line parsing. The "arg()" function accepts
        the following parameters:

        alias
            A single character alias.

        comment
            Required. Used to generate the usage/help message.

        default
            The value set when the option is not used.

            If this is a subroutine reference it will be called with a
            hashref containg all option/argument values after parsing the
            source has finished. The value to be set must be returned, and
            any changes to the hashref are ignored.

        hidden
            When true this option will not appear in usage messages unless
            the usage message is a help request.

            This is handy if you have developer-only options, or options
            that are very rarely used that you don't want cluttering up your
            normal usage message.

        isa Required. Is mapped to a Getopt::Long type according to the
            following table:

                isa              Getopt::Long
                ---              ------------
                 'ArrayRef'      's@'
                 'Flag'          '!'
                 'Bool'          '!'
                 'Counter'       '+'
                 'HashRef'       's%'
                 'Int'           '=i'
                 'Num'           '=f'
                 'Str'           '=s'

        isa_name
            When provided this parameter will be presented instead of the
            generic presentation for the 'isa' parameter.

        ishelp
            When true creates a trigger parameter that generates a usage
            message exception. In other words it is just a shortcut for the
            following:

                opt help => (
                    isa     => 'Flag',
                    alias   => 'h',
                    comment => 'print help message and exit',
                    trigger => sub {
                        my ( $cmd, $value ) = @_;
                        die $cmd->usage(OptArgs2::STYLE_FULL);
                    }
                );

            Note that this option conflicts with the trigger parameter.

        show_default
            If set to a true value then usage messages will show the default
            value.

        trigger
            The trigger parameter lets you define a subroutine that is
            called *immediately* as soon as the option presence is detected.
            This is primarily to support --help or --version options which
            typically don't need the full command line to be processed
            before generating a response.

                opt version => (
                    isa     => 'Flag',
                    alias   => 'V',
                    comment => 'print version string and exit',
                    trigger => sub {
                        my ( $cmd, $value ) = @_;
                        die "$cmd version $VERSION\n";
                    }
                );

            The trigger subref is passed two parameters: a OptArgs2::Cmd
            object and the value (if any) of the option. The OptArgs2::Cmd
            object is an internal one, but one public interface is has (in
            addition to the usage() method described in 'ishelp' above) is
            the usage_tree() method which gives a usage overview of all
            subcommands in the command hierarchy.

                opt usage_tree => (
                    isa     => 'Flag',
                    alias   => 'U',
                    comment => 'print usage tree and exit',
                    trigger => sub {
                        my ( $cmd, $value ) = @_;
                        die $cmd->usage_tree;
                    }
                );

                # demo COMMAND [OPTIONS...]
                #     demo foo ACTION [OPTIONS...]
                #     demo bar [OPTIONS...]

    optargs( [@argv] ) -> HASHref
        Parse @ARGV by default (or @argv when given) for the arguments and
        options defined for the *default global* command. Argument decoding
        and exceptions are the same as for "class_optargs", but this
        function returns only the combined argument/option values HASHref.

    subcmd( $class, %parameters ) -> OptArgs2::Cmd
        Defines a subcommand identified by $class which must include the
        name of a previously defined (sub)command + '::'.

        Accepts the same parameters as "cmd()" in addition to the following:

        hidden
            Hide the existence of this subcommand in usage messages created
            with OptArgs2::STYLE_NORMAL. This is handy if you have
            developer-only or rarely-used commands that you don't want
            cluttering up your normal usage message.

SEE ALSO
    Getopt::Long

    This module is duplicated on CPAN as Getopt::Args2, to cover both its
    original name and yet still be found in the mess that is Getopt::*.

SUPPORT & DEVELOPMENT
    This distribution is managed via github:

        https://github.com/mlawren/p5-OptArgs2/tree/devel

    This distribution follows the semantic versioning model:

        http://semver.org/

    Code is tidied up on Git commit using githook-perltidy:

        http://github.com/mlawren/githook-perltidy

AUTHOR
    Mark Lawrence <nomad@null.net>

LICENSE
    Copyright 2016 Mark Lawrence <nomad@null.net>

    This program is free software; you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by the
    Free Software Foundation; either version 3 of the License, or (at your
    option) any later version.

