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


version 1.10


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

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 the C<strict> parameter 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 several 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 function name indicates the type of option. The name argument is a string with the names and aliases separated by vertical bar characters.

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 thrown:

--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 = (


Sets the validation parameter(s) for an option.

@spec = (
Param("port")->valid(qr/\d+/), # regex validation
Param("config")->valid(sub { -r }), # custom validation
->valid(\&_valid_key, \&valid_value), # keypairs take two

See the "Validation" section, below, for more.


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" ),


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.


Sets the documentation string for an option.

@spec = (
Param("output")->doc("write output to the specified file"),

This string shows up in the "usage" method.

Validation happens in two stages. First, individual parameters may have validation criteria added to them. Second, the parsed options object may be validated by checking that all requirements collectively are met.

Parameter validation

The Param, List, and Keypair option types may be provided 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 consistency.

If no default is explicitly 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" option to the "validate" method should be used to force users to provide an explicit value.

# Must be provided and is thus always validated
@spec = ( Param("width")->valid(qr/\d+/) );
$opt = Getopt::Lucid->getopt(\@spec);
$opt->validate( {requires => ['width']} );

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.

Older versions of Getopt::Lucid used validation arguments provided in the Spec constructor. This is still supported, but is deprecated and discouraged. It may be removed in a future version of Getopt::Lucid.

# deprecated
Param("height", qr/\d+/)

Options object validation

The "validate" method should be called on the result of "getopt". This will check that all parameter prerequisites defined by "needs" have been met. It also takes a hashref of arguments. The optional "requires" argument gives an arrayref of parameters that must exist.

The reason that object validation is done separate from "getopt" is to allow for better control over different options that might be required or to allow some dependencies (i.e. from "needs") to be met via a configuration file.

@spec = (
Param("action")->needs(qw/user password/),
$opt = Getopt::Lucid->getopt(\@spec);
$opt->merge_defaults( read_config() ); # provides 'user' & 'password'
$opt->validate({requires => ['action']});

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

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

@spec = (
$opt = Getopt::Lucid->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.

List and Keypair options are returned as flattened lists:

my @lib = $opt->get_lib;
my %define = $opt->get_define;

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 array

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 subclasses:

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

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

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. The final argument may be a hashref of parameters. The only valid parameter currently is:

strict -- enables strict mode when true

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.

$opt->validate( \%arguments );

Takes an optional argument hashref, validates that all requirements and prerequisites are met or throws an error. Valid argument keys are:

"requires" -- an arrayref of options that must exist in the options object.

This method returns the object for convenient chaining:

$opt = Getopt::Lucid->getopt(\@spec)->validate;

%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 preexisting value. For Counter options, the value is added to any preexisting 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 key/value pairs 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.

For convenience, C<getopts()> is a alias for C<getopt()>.

%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 preexisting 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 processing.

%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" call.

Returns a string of usage information derived from the options spec, including any "doc" modifiers. Because invalid options throw exceptions, if you want to provide usage, you should separately invoke "new" and "getopt"

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


In 1.00, the following API changes have been made:

"new()" now takes an optional hashref of parameters as the last argument

The global $STRICT variable has been replaced with a per-object parameter "strict"

The "required" modifier has been removed and a new "validate" method has been added to facilitate late/custom checks of required options








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.


Bugs / Feature Requests
Please report any bugs or feature requests through the issue tracker at <>. You will be notified automatically of any progress on your issue.

Source Code
This is open source software. The code repository is available for public review and contribution under the terms of the license.


git clone


David Golden <dagolden AT cpan DOT org>


Chris White <cxwembedded AT gmail DOT com>

David Golden <xdg AT xdg DOT me>

David Precious <davidp AT preshweb DOT co DOT uk>

James E Keenan <jkeenan AT cpan DOT org>

Kevin McGrath <kmcgrath AT cpan DOT org>

Nova Patch <patch AT cpan DOT org>

Robert Bohne <rbo AT cpan DOT org>

thilp <thilp AT thilp DOT net>


This software is Copyright (c) 2019 by David Golden.

This is free software, licensed under:

The Apache License, Version 2.0, January 2004