(Perl) Clear, readable syntax for command line processing
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    Getopt::Lucid - Clear, readable syntax for command line processing

    This documentation describes version 0.19.

       use Getopt::Lucid qw( :all );
   # basic option specifications with aliases
   @specs = (
   $opt = Getopt::Lucid->getopt( \@specs );
   $verbosity = $opt->get_verbose;
       @libs = $opt->get_lib;
       %defs = $opt->get_define;
   %all_options = $opt->options;
   # advanced option specifications
   @adv_spec = (
         Param("input")->required,          # required
         Param("mode")->default("tcp"),     # defaults
         Param("host")->needs("port"),      # dependencies
         Param("port", qr/\d+/ ),           # regex validation
         Param("config", sub { -r } ),      # custom validation
         Param("help")->anycase,            # case insensitivity
   # example with a config file
   use Config::Std;
       if ( -r $opt->get_config ) {
         read_config( $opt->get_config() => my %config_hash );
         $opt->merge_defaults( $config_hash{''} ); 

    The goal of this module is providing good code readability and clarity
    of intent for command-line option processing. While readability is a
    subjective standard, Getopt::Lucid relies on a more verbose,
    plain-English option specification as compared against the more symbolic
    approach of Getopt::Long. Key features include:

    *   Five option types: switches, counters, parameters, lists, and

    *   Three option styles: long, short (including bundled), and bare
        (without dashes)

    *   Specification of defaults, required options and option dependencies

    *   Validation of options with regexes or subroutines

    *   Negation of options on the command line

    *   Support for parsing any array, not just the default @ARGV

    *   Incorporation of external defaults (e.g. from a config file) with
        user control of precedence

  Option Styles, Naming and "Strictness"
    Getopt::Lucid support three kinds of option styles: long-style
    ("--foo"), short-style ("-f") and bareword style ("foo"). Short-style
    options are automatically unbundled during command line processing if a
    single dash is followed by more than one letter (e.g. "-xzf" becomes "-x
    -z -f" ).

    Each option is identified in the specification with a string consisting
    of the option "name" followed by zero or more "aliases", with any alias
    (and each subsequent alias) separated by a vertical bar character. E.g.:

       "lib|l|I" means name "lib", alias "l" and alias "I"

    Names and aliases must begin with an alphanumeric character, but
    subsequently may also include both underscore and dash. (E.g. both
    "input-file" and "input_file" are valid.) While names and aliases are
    interchangeable when provided on the command line, the "name" portion is
    used with the accessors for each option (see "Accessors and Mutators").

    Any of the names and aliases in the specification may be given in any of
    the three styles. By default, Getopt::Lucid works in "magic" mode, in
    which option names or aliases may be specified with or without leading
    dashes, and will be parsed from the command line whether or not they
    have corresponding dashes. Single-character names or aliases may be read
    with no dash, one dash or two dashes. Multi-character names or aliases
    must have either no dashes or two dashes. E.g.:

    *   Both "foo" and "--foo" as names in the specification may be read
        from the command line as either "--foo" or "foo"

    *   The specification name "f" may be read from the command line as
        "--f", "-f", or just "f"

    In practice, this means that the specification need not use dashes, but
    if used on the command line, they will be treated appropriately.

    Alternatively, Getopt::Lucid can operate in "strict" mode by setting
    $Getopt::Lucid::STRICT to a true value. In strict mode, option names and
    aliases may still be specified in any of the three styles, but they will
    only be parsed from the command line if they are used in exactly the
    same style. E.g., given the name and alias "--help|-h", only "--help"
    and "-h" are valid for use on the command line.

  Option Specification Constructors
    Options specifications are provided to Getopt::Lucid in an array.
    Entries in the array must be created with one of five special
    constructor functions that return a specification object. These
    constructor functions may be imported either individually or as a group
    using the import tag ":all" (e.g. "use Getopt::Lucid qw(:all);").

    The form of the constructor is:


    The constructor name indicates the type of option. The name argument is
    a string with the names and aliases separated by vertical bar
    characters. Validation arguments may or may not be relevant, depending
    on the type of option. (See "Validation" below.)

    The five option specification constructors are:

    A true/false value. Defaults to false. The appearance of an option of
    this type on the command line sets it to true.

    A numerical counter. Defaults to 0. The appearance of an option of this
    type on the command line increments the counter by one.

    A variable taking an argument. Defaults to "" (the empty string). When
    an option of this type appears on the command line, the value of the
    option is set in one of two ways -- appended with an equals sign or from
    the next argument on the command line:

       --name value

    In the case where white space is used to separate the option name and
    the value, if the value looks like an option, an exception will be

       --name --value        # throws an exception

    This is like "Param()" but arguments are pushed onto a list. The default
    list is empty.

    A variable taking an argument pair, which are added to a hash. Arguments
    are handled as with "Param()", but the argument itself must have a key
    and value joined by an equals sign.

       --name key=value

  Option modifiers
    An option specification can be further modified with the following
    methods, each of which return the object modified so that modifier
    chaining is possible. E.g.:

       @spec = (

    Changes the default for the option to the argument(s) of "default()".
    List and hashes can take either a list or a reference to an array or
    hash, respectively.

       @spec = (
         List("dirs")->default(qw( /var /home )),
         Keypair("define")->default( arch => "i386" ),

    Indicates that the option *must* appear on the command line or else an
    exception is thrown. No argument is needed.

       @spec = (

    Takes as an argument a list of option names or aliases of dependencies.
    If the option this modifies appears on the command line, each of the
    options given as an argument must appear on the command line as well or
    an exception is thrown.

       @spec = (

    Indicates that the associated option names/aliases may appear on the
    command line in lowercase, uppercase, or any mixture of the two. No
    argument is needed.

       @spec = (
         Switch("help|h")->anycase(),    # "Help", "HELP", etc.

    For Param, List, and Keypair option types, the constructor may be passed
    an optional validation specification. Values provided on the command
    line will be validated according to the specification or an exception
    will be thrown.

    A validation specification can be either a regular expression, or a
    reference to a subroutine. Keypairs take up to two validation
    specifiers. The first is applied to keys and the second is applied to
    values; either can be left undef to ignore validation. (More complex
    validation of specific values for specific keys must be done manually.)

    Validation is also applied to default values provided via the
    "default()" modifier or later modified with "append_defaults",
    "merge_defaults", or "replace_defaults". This ensures internal

    If no default is explictly provided, validation is only applied if the
    option appears on the command line. (In other words, the built-in
    defaults are always considered valid if the option does not appear.) If
    this is not desired, the "required()" modifier should be used to force
    users to provide an explicit value.

       # Must be provided and is thus always validated
       Param("width",  qr/\d+/)->required 
   # Can be left blank, but is validated if provided
       Param("height", qr/\d+/)

    For validation subroutines, the value found on the command line is
    passed as the first element of @_, and $_ is also set equal to the first
    element. (N.B. Changing $_ will not change the value that is captured.)
    The value validates if the subroutine returns a true value.

    For validation with regular expressions, consider using Regexp::Common
    for a ready library of validation options.

  Parsing the Command Line
    Technically, Getopt::Lucid scans an array for command line options, not
    a command-line string. By default, this array is @ARGV (though other
    arrays can be used -- see "new()"), which is typically provided by the
    operating system according to system-specific rules.

    When Getopt::Lucid processes the array, it scans the array in order,
    removing any specified command line options and any associated
    arguments, and leaving behind any unrecognized elements in the array. If
    an element consisting solely of two-dashes ("--") is found, array
    scanning is terminated at that point. Any options found during scanning
    are applied in order. E.g.:

       @ARGV = qw( --lib /tmp --lib /var );
       my $opt = Getopt::Lucid->getopt( [ List("lib") ] );
       print join ", " $opt->lib;
       # prints "/tmp, /var"

    If an element encountered in processing begins with a dash, but is not
    recognized as a short-form or long-form option name or alias, an
    exception will be thrown.

    Getopt::Lucid also supports negating options. Options are negated if the
    option is specified with "no-" or "--no-" prefixed to a name or alias.
    By default, negation clears the option: Switch and Counter options are
    set to zero; Param options are set to ""; List and Keypair options are
    set to an empty list and empty hash, respectively. For List and Keypair
    options, it is also possible to negate a specific list element or hash
    key by placing an equals sign and the list element or key immediately
    after the option name:

       --no-lib=/tmp --no-define=arch
       # removes "/tmp" from lib and the "arch" key from define

    As with all options, negation is processed in order, allowing a "reset"
    in the middle of command line processing. This may be useful for those
    using command aliases who wish to "switch off" options in the alias.
    E.g, in unix:

       $ alias wibble = wibble.pl --verbose
       $ wibble --no-verbose
   # @ARGV would contain ( "--verbose", "--no-verbose" )

    This also may have applications in post-processing configuration files
    (see "Managing Defaults and Config Files").

  Accessors and Mutators
    After processing the command-line array, the values of the options may
    be read or modified using accessors/mutators of the form "get_NAME" and
    "set_NAME", where NAME represents the option name in the specification
    without any leading dashes. E.g.

       @spec = (
   $opt = Getopt::Long->getopt( \@spec );
       print $opt->get_test ? "True" : "False";

    For option names with dashes, underscores should be substitued in the
    accessor calls. E.g.

       @spec = (
   $opt = Getopt::Long->getopt( \@spec );
       print $opt->get_input_file;

    This can create an ambiguous case if a similar option exists with
    underscores in place of dashes. (E.g. "input_file" and "input-file".)
    Users can safely avoid these problems by choosing to use either dashes
    or underscores exclusively and not mixing the two styles.

    Using the "set_NAME" mutator is not recommended and should be used with
    caution. No validation is performed and changes will be lost if the
    results of processing the command line array are recomputed (e.g, such
    as occurs if new defaults are applied). List and Keypair options
    mutators take a list, not references.

  Managing Defaults and Config Files
    A typical problem for command-line option processing is the precedence
    relationship between default option values specified within the program,
    default option values stored in a configuration file or in environment
    variables, and option values specified on the command-line, particularly
    when the command-line specifies an alternate configuration file.

    Getopt::Lucid takes the following approach to this problem:

    *   Initial default values may be specified as part of the option
        specification (using the "default()" modifier)

    *   Default values from the option specification may be modified or
        replaced entirely with default values provided in an external hash
        (such as from a standard config file or environment variables)

    *   When the command-line array is processed, options and their
        arguments are stored in the order they appeared in the command-line

    *   The stored options are applied in-order to modify or replace the set
        of "current" default option values

    *   If default values are subsequently changed (such as from an
        alternative configuration file), the stored options are re-applied
        in-order to the new set of default option values

    With this approach, the resulting option set is always the result of
    applying options (or negations) from the command-line array to a set of
    default-values. Users have complete freedom to apply whatever precedence
    rules they wish to the default values and may even change default values
    after the command-line array is processed without losing the options
    given on the command line.

    Getopt::Lucid provides several functions to assist in manipulating
    default values:

    *   "merge_defaults()" -- new defaults overwrite any matching, existing
        defaults. KeyPairs hashes and List arrays are replaced entirely with
        new defaults

    *   "append_defaults()" -- new defaults overwrite any matching, existing
        defaults, except for Counter and List options, which have the new
        defaults added and appended, respectively, and KeyPair options,
        which are flattened into any existing default hash

    *   "replace_defaults()" -- new defaults replace existing defaults; any
        options not provided in the new defaults are reset to zero/empty,
        ignoring any default given in the option specification

    *   "reset_defaults()" -- returns defaults to values given in the
        options specification

  Exceptions and Error Handling
    Getopt::Lucid uses Exception::Class for exceptions. When a major error
    occurs, Getopt::Lucid will die and throw one of three Exception::Class

    *   "Getopt::Lucid::Exception::Usage" -- thrown when Getopt::Lucid
        methods are called incorrectly

    *   "Getopt::Lucid::Exception::Spec" -- thrown when the specification
        array contains incorrect or invalid data

    *   "Getopt::Lucid::Exception::ARGV" -- thrown when the command-line is
        processed and fails to pass specified validation, requirements, or
        is otherwise determined to be invalid

    These exception may be caught using an "eval" block and allow the
    calling program to respond differently to each class of exception.

       my $opt;
       eval { $opt = Getopt::Lucid->getopt( \@spec ) };
       if ($@) {
         print "$@\n" && print_usage() && exit 1
           if ref $@ eq 'Getopt::Lucid::Exception::ARGV';
         ref $@ ? $@->rethrow : die $@;

  Ambiguous Cases and Gotchas
   One-character aliases and anycase
       @spec = (

    Consider the spec above. By specifying "anycase" on these, "verbose",
    "Verbose", "VERBOSE" are all acceptable, as are "version", "Version" and
    so on. (Including long-form versions of these, too, if "magic" mode is
    used.) However, what if the command line has "-v" or even "-v -V"? In
    this case, the rule is that exact case matches are used before
    case-insensitive matches are searched. Thus, "-v" can only match
    "verbose", despite the "anycase" modification, and likewise "-V" can
    only match "version".

   Identical names except for dashes and underscores
       @spec = (

    Consider the spec above. These are two, separate, valid options, but a
    call to the accessor "get_input_file" is ambiguous and may return either
    option, depending on which first satisfies a "fuzzy-matching" algorithm
    inside the accessor code. Avoid identical names with mixed dash and
    underscore styles.

      $opt = Getopt::Lucid->new( \@option_spec );
      $opt = Getopt::Lucid->new( \@option_spec, \@option_array );

    Creates a new Getopt::Lucid object. An array reference to an option spec
    is required as an argument. (See "USAGE" for a description of the object
    spec). By default, objects will be set to read @ARGV for command line
    options. An optional second argument with a reference to an array will
    use that array for option processing instead. For typical cases, users
    will likely prefer to call "getopt" instead, which creates a new object
    and parses the command line with a single function call.

      %options = append_defaults( %config_hash );
      %options = append_defaults( \%config_hash );

    Takes a hash or hash reference of new default values, modifies the
    stored defaults, recalculates the result of processing the command line
    with the revised defaults, and returns a hash with the resulting
    options. Each key/value pair in the passed hash is added to the stored
    defaults. For Switch and Param options, the value in the passed hash
    will overwrite any pre-existing value. For Counter options, the value is
    added to any pre-existing value. For List options, the value (or values,
    if the value is an array reference) will be pushed onto the end of the
    list of existing values. For Keypair options, the keypairs will be added
    to the existing hash, overwriting existing key/value pairs (just like
    merging two hashes). Keys which are not valid names from the options
    specification will be ignored.

      %defaults = $opt->defaults();

    Returns a hash containing current default values. Keys are names from
    the option specification (without any leading dashes). These defaults
    represent the baseline values that are modified by the parsed command
    line options.

      $opt = Getopt::Lucid->getopt( \@option_spec );
      $opt = Getopt::Lucid->getopt( \@option_spec, \@option_array );

    Parses the command line array (@ARGV by default). When called as a class
    function, "getopt" takes the same arguments as "new", calls "new" to
    create an object before parsing the command line, and returns the new
    object. When called as an object method, it takes no arguments and
    returns itself.

      %options = merge_defaults( %config_hash );
      %options = merge_defaults( \%config_hash );

    Takes a hash or hash reference of new default values, modifies the
    stored defaults, recalculates the result of processing the command line
    with the revised defaults, and returns a hash with the resulting
    options. Each key/value pair in the passed hash is added to the stored
    defaults, overwriting any pre-existing value. Keys which are not valid
    names from the options specification will be ignored.

      @names = $opt->names();

    Returns the list of names in the options specification. Each name
    represents a key in the hash of options provided by "options".

      %options = $opt->options();

    Returns a deep copy of the options hash. Before "getopt" is called, its
    behavior is undefined. After "getopt" is called, this will return the
    result of modifying the defaults with the results of command line

      %options = replace_defaults( %config_hash );
      %options = replace_defaults( \%config_hash );

    Takes a hash or hash reference of new default values, replaces the
    stored defaults, recalculates the result of processing the command line
    with the revised defaults, and returns a hash with the resulting
    options. Each key/value pair in the passed hash replaces existing
    defaults, including those given in the option specifications. Keys which
    are not valid names from the option specification will be ignored.

      %options = reset_defaults();

    Resets the stored defaults to the original values from the options
    specification, recalculates the result of processing the command line
    with the restored defaults, and returns a hash with the resulting
    options. This undoes the effect of a "merge_defaults" or "add_defaults"

    *   Config::Tiny

    *   Config::Simple

    *   Config::Std

    *   Getopt::Long

    *   Regexp::Common

    Please report any bugs or feature using the CPAN Request Tracker. Bugs
    can be submitted through the web interface at

    When submitting a bug or request, please include a test-file or a patch
    to an existing test-file that illustrates the bug or desired feature.

    David A. Golden (DAGOLDEN)

    Copyright (c) 2005 - 2009 by David A. Golden

    Licensed under the Apache License, Version 2.0 (the "License"); you may
    not use this file except in compliance with the License. You may obtain
    a copy of the License at <http://www.apache.org/licenses/LICENSE-2.0>

    Files produced as output though the use of this software shall not be
    considered Derivative Works, but shall be considered the original work
    of the Licensor.

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.