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       Getopt::Long - Extended processing of command line options


         use Getopt::Long;
         my $data   = "file.dat";
         my $length = 24;
         my $verbose;
         GetOptions ("length=i" => \$length,    # numeric
                     "file=s"   => \$data,      # string
                     "verbose"  => \$verbose)   # flag
         or die("Error in command line arguments\n");


       The Getopt::Long module implements an extended getopt function called GetOptions(). It
       parses the command line from @ARGV, recognizing and removing specified options and their
       possible values.

       This function adheres to the POSIX syntax for command line options, with GNU extensions.
       In general, this means that options have long names instead of single letters, and are
       introduced with a double dash "--". Support for bundling of command line options, as was
       the case with the more traditional single-letter approach, is provided but not enabled by

Command Line Options, an Introduction

       Command line operated programs traditionally take their arguments from the command line,
       for example filenames or other information that the program needs to know. Besides
       arguments, these programs often take command line options as well. Options are not
       necessary for the program to work, hence the name 'option', but are used to modify its
       default behaviour. For example, a program could do its job quietly, but with a suitable
       option it could provide verbose information about what it did.

       Command line options come in several flavours. Historically, they are preceded by a single
       dash "-", and consist of a single letter.

           -l -a -c

       Usually, these single-character options can be bundled:


       Options can have values, the value is placed after the option character. Sometimes with
       whitespace in between, sometimes not:

           -s 24 -s24

       Due to the very cryptic nature of these options, another style was developed that used
       long names. So instead of a cryptic "-l" one could use the more descriptive "--long". To
       distinguish between a bundle of single-character options and a long one, two dashes are
       used to precede the option name. Early implementations of long options used a plus "+"
       instead. Also, option values could be specified either like



           --size 24

       The "+" form is now obsolete and strongly deprecated.

Getting Started with Getopt::Long

       Getopt::Long is the Perl5 successor of "". This was the first Perl module that
       provided support for handling the new style of command line options, in particular long
       option names, hence the Perl5 name Getopt::Long. This module also supports single-
       character options and bundling.

       To use Getopt::Long from a Perl program, you must include the following line in your Perl

           use Getopt::Long;

       This will load the core of the Getopt::Long module and prepare your program for using it.
       Most of the actual Getopt::Long code is not loaded until you really call one of its

       In the default configuration, options names may be abbreviated to uniqueness, case does
       not matter, and a single dash is sufficient, even for long option names. Also, options may
       be placed between non-option arguments. See "Configuring Getopt::Long" for more details on
       how to configure Getopt::Long.

   Simple options
       The most simple options are the ones that take no values. Their mere presence on the
       command line enables the option. Popular examples are:

           --all --verbose --quiet --debug

       Handling simple options is straightforward:

           my $verbose = '';   # option variable with default value (false)
           my $all = '';       # option variable with default value (false)
           GetOptions ('verbose' => \$verbose, 'all' => \$all);

       The call to GetOptions() parses the command line arguments that are present in @ARGV and
       sets the option variable to the value 1 if the option did occur on the command line.
       Otherwise, the option variable is not touched. Setting the option value to true is often
       called enabling the option.

       The option name as specified to the GetOptions() function is called the option
       specification. Later we'll see that this specification can contain more than just the
       option name. The reference to the variable is called the option destination.

       GetOptions() will return a true value if the command line could be processed successfully.
       Otherwise, it will write error messages using die() and warn(), and return a false result.

   A little bit less simple options
       Getopt::Long supports two useful variants of simple options: negatable options and
       incremental options.

       A negatable option is specified with an exclamation mark "!" after the option name:

           my $verbose = '';   # option variable with default value (false)
           GetOptions ('verbose!' => \$verbose);

       Now, using "--verbose" on the command line will enable $verbose, as expected. But it is
       also allowed to use "--noverbose", which will disable $verbose by setting its value to 0.
       Using a suitable default value, the program can find out whether $verbose is false by
       default, or disabled by using "--noverbose".

       An incremental option is specified with a plus "+" after the option name:

           my $verbose = '';   # option variable with default value (false)
           GetOptions ('verbose+' => \$verbose);

       Using "--verbose" on the command line will increment the value of $verbose. This way the
       program can keep track of how many times the option occurred on the command line. For
       example, each occurrence of "--verbose" could increase the verbosity level of the program.

   Mixing command line option with other arguments
       Usually programs take command line options as well as other arguments, for example, file
       names. It is good practice to always specify the options first, and the other arguments
       last. Getopt::Long will, however, allow the options and arguments to be mixed and 'filter
       out' all the options before passing the rest of the arguments to the program. To stop
       Getopt::Long from processing further arguments, insert a double dash "--" on the command

           --size 24 -- --all

       In this example, "--all" will not be treated as an option, but passed to the program
       unharmed, in @ARGV.

   Options with values
       For options that take values it must be specified whether the option value is required or
       not, and what kind of value the option expects.

       Three kinds of values are supported: integer numbers, floating point numbers, and strings.

       If the option value is required, Getopt::Long will take the command line argument that
       follows the option and assign this to the option variable. If, however, the option value
       is specified as optional, this will only be done if that value does not look like a valid
       command line option itself.

           my $tag = '';       # option variable with default value
           GetOptions ('tag=s' => \$tag);

       In the option specification, the option name is followed by an equals sign "=" and the
       letter "s". The equals sign indicates that this option requires a value. The letter "s"
       indicates that this value is an arbitrary string. Other possible value types are "i" for
       integer values, and "f" for floating point values. Using a colon ":" instead of the equals
       sign indicates that the option value is optional. In this case, if no suitable value is
       supplied, string valued options get an empty string '' assigned, while numeric options are
       set to 0.

   Options with multiple values
       Options sometimes take several values. For example, a program could use multiple
       directories to search for library files:

           --library lib/stdlib --library lib/extlib

       To accomplish this behaviour, simply specify an array reference as the destination for the

           GetOptions ("library=s" => \@libfiles);

       Alternatively, you can specify that the option can have multiple values by adding a "@",
       and pass a scalar reference as the destination:

           GetOptions ("library=s@" => \$libfiles);

       Used with the example above, @libfiles (or @$libfiles) would contain two strings upon
       completion: "lib/stdlib" and "lib/extlib", in that order. It is also possible to specify
       that only integer or floating point numbers are acceptable values.

       Often it is useful to allow comma-separated lists of values as well as multiple
       occurrences of the options. This is easy using Perl's split() and join() operators:

           GetOptions ("library=s" => \@libfiles);
           @libfiles = split(/,/,join(',',@libfiles));

       Of course, it is important to choose the right separator string for each purpose.

       Warning: What follows is an experimental feature.

       Options can take multiple values at once, for example

           --coordinates 52.2 16.4 --rgbcolor 255 255 149

       This can be accomplished by adding a repeat specifier to the option specification. Repeat
       specifiers are very similar to the "{...}" repeat specifiers that can be used with regular
       expression patterns.  For example, the above command line would be handled as follows:

           GetOptions('coordinates=f{2}' => \@coor, 'rgbcolor=i{3}' => \@color);

       The destination for the option must be an array or array reference.

       It is also possible to specify the minimal and maximal number of arguments an option
       takes. "foo=s{2,4}" indicates an option that takes at least two and at most 4 arguments.
       "foo=s{1,}" indicates one or more values; "foo:s{,}" indicates zero or more option values.

   Options with hash values
       If the option destination is a reference to a hash, the option will take, as value,
       strings of the form key"="value. The value will be stored with the specified key in the

           GetOptions ("define=s" => \%defines);

       Alternatively you can use:

           GetOptions ("define=s%" => \$defines);

       When used with command line options:

           --define os=linux --define vendor=redhat

       the hash %defines (or %$defines) will contain two keys, "os" with value "linux" and
       "vendor" with value "redhat". It is also possible to specify that only integer or floating
       point numbers are acceptable values. The keys are always taken to be strings.

   User-defined subroutines to handle options
       Ultimate control over what should be done when (actually: each time) an option is
       encountered on the command line can be achieved by designating a reference to a subroutine
       (or an anonymous subroutine) as the option destination. When GetOptions() encounters the
       option, it will call the subroutine with two or three arguments. The first argument is the
       name of the option. (Actually, it is an object that stringifies to the name of the
       option.) For a scalar or array destination, the second argument is the value to be stored.
       For a hash destination, the second argument is the key to the hash, and the third argument
       the value to be stored. It is up to the subroutine to store the value, or do whatever it
       thinks is appropriate.

       A trivial application of this mechanism is to implement options that are related to each
       other. For example:

           my $verbose = '';   # option variable with default value (false)
           GetOptions ('verbose' => \$verbose,
                       'quiet'   => sub { $verbose = 0 });

       Here "--verbose" and "--quiet" control the same variable $verbose, but with opposite

       If the subroutine needs to signal an error, it should call die() with the desired error
       message as its argument. GetOptions() will catch the die(), issue the error message, and
       record that an error result must be returned upon completion.

       If the text of the error message starts with an exclamation mark "!"  it is interpreted
       specially by GetOptions(). There is currently one special command implemented:
       "die("!FINISH")" will cause GetOptions() to stop processing options, as if it encountered
       a double dash "--".

       In version 2.37 the first argument to the callback function was changed from string to
       object. This was done to make room for extensions and more detailed control. The object
       stringifies to the option name so this change should not introduce compatibility problems.

       Here is an example of how to access the option name and value from within a subroutine:

           GetOptions ('opt=i' => \&handler);
           sub handler {
               my ($opt_name, $opt_value) = @_;
               print("Option name is $opt_name and value is $opt_value\n");

   Options with multiple names
       Often it is user friendly to supply alternate mnemonic names for options. For example
       "--height" could be an alternate name for "--length". Alternate names can be included in
       the option specification, separated by vertical bar "|" characters. To implement the above

           GetOptions ('length|height=f' => \$length);

       The first name is called the primary name, the other names are called aliases. When using
       a hash to store options, the key will always be the primary name.

       Multiple alternate names are possible.

   Case and abbreviations
       Without additional configuration, GetOptions() will ignore the case of option names, and
       allow the options to be abbreviated to uniqueness.

           GetOptions ('length|height=f' => \$length, "head" => \$head);

       This call will allow "--l" and "--L" for the length option, but requires a least "--hea"
       and "--hei" for the head and height options.

   Summary of Option Specifications
       Each option specifier consists of two parts: the name specification and the argument

       The name specification contains the name of the option, optionally followed by a list of
       alternative names separated by vertical bar characters.

           length            option name is "length"
           length|size|l     name is "length", aliases are "size" and "l"

       The argument specification is optional. If omitted, the option is considered boolean, a
       value of 1 will be assigned when the option is used on the command line.

       The argument specification can be

       !   The option does not take an argument and may be negated by prefixing it with "no" or
           "no-". E.g. "foo!" will allow "--foo" (a value of 1 will be assigned) as well as
           "--nofoo" and "--no-foo" (a value of 0 will be assigned). If the option has aliases,
           this applies to the aliases as well.

           Using negation on a single letter option when bundling is in effect is pointless and
           will result in a warning.

       +   The option does not take an argument and will be incremented by 1 every time it
           appears on the command line. E.g. "more+", when used with "--more --more --more", will
           increment the value three times, resulting in a value of 3 (provided it was 0 or
           undefined at first).

           The "+" specifier is ignored if the option destination is not a scalar.

       = type [ desttype ] [ repeat ]
           The option requires an argument of the given type. Supported types are:

           s   String. An arbitrary sequence of characters. It is valid for the argument to start
               with "-" or "--".

           i   Integer. An optional leading plus or minus sign, followed by a sequence of digits.

           o   Extended integer, Perl style. This can be either an optional leading plus or minus
               sign, followed by a sequence of digits, or an octal string (a zero, optionally
               followed by '0', '1', .. '7'), or a hexadecimal string ("0x" followed by '0' ..
               '9', 'a' .. 'f', case insensitive), or a binary string ("0b" followed by a series
               of '0' and '1').

           f   Real number. For example 3.14, "-6.23E24" and so on.

           The desttype can be "@" or "%" to specify that the option is list or a hash valued.
           This is only needed when the destination for the option value is not otherwise
           specified. It should be omitted when not needed.

           The repeat specifies the number of values this option takes per occurrence on the
           command line. It has the format "{" [ min ] [ "," [ max ] ] "}".

           min denotes the minimal number of arguments. It defaults to 1 for options with "=" and
           to 0 for options with ":", see below. Note that min overrules the "=" / ":" semantics.

           max denotes the maximum number of arguments. It must be at least min. If max is
           omitted, but the comma is not, there is no upper bound to the number of argument
           values taken.

       : type [ desttype ]
           Like "=", but designates the argument as optional.  If omitted, an empty string will
           be assigned to string values options, and the value zero to numeric options.

           Note that if a string argument starts with "-" or "--", it will be considered an
           option on itself.

       : number [ desttype ]
           Like ":i", but if the value is omitted, the number will be assigned.

       : + [ desttype ]
           Like ":i", but if the value is omitted, the current value for the option will be

Advanced Possibilities

   Object oriented interface
       Getopt::Long can be used in an object oriented way as well:

           use Getopt::Long;
           $p = Getopt::Long::Parser->new;
           $p->configure(...configuration options...);
           if ($p->getoptions(...options descriptions...)) ...
           if ($p->getoptionsfromarray( \@array, ...options descriptions...)) ...

       Configuration options can be passed to the constructor:

           $p = new Getopt::Long::Parser
                    config => [...configuration options...];

   Thread Safety
       Getopt::Long is thread safe when using ithreads as of Perl 5.8.  It is not thread safe
       when using the older (experimental and now obsolete) threads implementation that was added
       to Perl 5.005.

   Documentation and help texts
       Getopt::Long encourages the use of Pod::Usage to produce help messages. For example:

           use Getopt::Long;
           use Pod::Usage;

           my $man = 0;
           my $help = 0;

           GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
           pod2usage(1) if $help;
           pod2usage(-exitval => 0, -verbose => 2) if $man;


           =head1 NAME

           sample - Using Getopt::Long and Pod::Usage

           =head1 SYNOPSIS

           sample [options] [file ...]

              -help            brief help message
              -man             full documentation

           =head1 OPTIONS

           =over 8

           =item B<-help>

           Print a brief help message and exits.

           =item B<-man>

           Prints the manual page and exits.


           =head1 DESCRIPTION

           B<This program> will read the given input file(s) and do something
           useful with the contents thereof.


       See Pod::Usage for details.

   Parsing options from an arbitrary array
       By default, GetOptions parses the options that are present in the global array @ARGV. A
       special entry "GetOptionsFromArray" can be used to parse options from an arbitrary array.

           use Getopt::Long qw(GetOptionsFromArray);
           $ret = GetOptionsFromArray(\@myopts, ...);

       When used like this, options and their possible values are removed from @myopts, the
       global @ARGV is not touched at all.

       The following two calls behave identically:

           $ret = GetOptions( ... );
           $ret = GetOptionsFromArray(\@ARGV, ... );

       This also means that a first argument hash reference now becomes the second argument:

           $ret = GetOptions(\%opts, ... );
           $ret = GetOptionsFromArray(\@ARGV, \%opts, ... );

   Parsing options from an arbitrary string
       A special entry "GetOptionsFromString" can be used to parse options from an arbitrary

           use Getopt::Long qw(GetOptionsFromString);
           $ret = GetOptionsFromString($string, ...);

       The contents of the string are split into arguments using a call to
       "Text::ParseWords::shellwords". As with "GetOptionsFromArray", the global @ARGV is not

       It is possible that, upon completion, not all arguments in the string have been processed.
       "GetOptionsFromString" will, when called in list context, return both the return status
       and an array reference to any remaining arguments:

           ($ret, $args) = GetOptionsFromString($string, ... );

       If any arguments remain, and "GetOptionsFromString" was not called in list context, a
       message will be given and "GetOptionsFromString" will return failure.

       As with GetOptionsFromArray, a first argument hash reference now becomes the second

   Storing options values in a hash
       Sometimes, for example when there are a lot of options, having a separate variable for
       each of them can be cumbersome. GetOptions() supports, as an alternative mechanism,
       storing options values in a hash.

       To obtain this, a reference to a hash must be passed as the first argument to
       GetOptions(). For each option that is specified on the command line, the option value will
       be stored in the hash with the option name as key. Options that are not actually used on
       the command line will not be put in the hash, on other words, "exists($h{option})" (or
       defined()) can be used to test if an option was used. The drawback is that warnings will
       be issued if the program runs under "use strict" and uses $h{option} without testing with
       exists() or defined() first.

           my %h = ();
           GetOptions (\%h, 'length=i');       # will store in $h{length}

       For options that take list or hash values, it is necessary to indicate this by appending
       an "@" or "%" sign after the type:

           GetOptions (\%h, 'colours=s@');     # will push to @{$h{colours}}

       To make things more complicated, the hash may contain references to the actual
       destinations, for example:

           my $len = 0;
           my %h = ('length' => \$len);
           GetOptions (\%h, 'length=i');       # will store in $len

       This example is fully equivalent with:

           my $len = 0;
           GetOptions ('length=i' => \$len);   # will store in $len

       Any mixture is possible. For example, the most frequently used options could be stored in
       variables while all other options get stored in the hash:

           my $verbose = 0;                    # frequently referred
           my $debug = 0;                      # frequently referred
           my %h = ('verbose' => \$verbose, 'debug' => \$debug);
           GetOptions (\%h, 'verbose', 'debug', 'filter', 'size=i');
           if ( $verbose ) { ... }
           if ( exists $h{filter} ) { ... option 'filter' was specified ... }

       With bundling it is possible to set several single-character options at once. For example
       if "a", "v" and "x" are all valid options,


       will set all three.

       Getopt::Long supports three styles of bundling. To enable bundling, a call to
       Getopt::Long::Configure is required.

       The simplest style of bundling can be enabled with:

           Getopt::Long::Configure ("bundling");

       Configured this way, single-character options can be bundled but long options must always
       start with a double dash "--" to avoid ambiguity. For example, when "vax", "a", "v" and
       "x" are all valid options,


       will set "a", "v" and "x", but


       will set "vax".

       The second style of bundling lifts this restriction. It can be enabled with:

           Getopt::Long::Configure ("bundling_override");

       Now, "-vax" will set the option "vax".

       In all of the above cases, option values may be inserted in the bundle. For example:


       is equivalent to

           -h 24 -w 80

       A third style of bundling allows only values to be bundled with options. It can be enabled

           Getopt::Long::Configure ("bundling_values");

       Now, "-h24" will set the option "h" to 24, but option bundles like "-vxa" and "-h24w80"
       are flagged as errors.

       Enabling "bundling_values" will disable the other two styles of bundling.

       When configured for bundling, single-character options are matched case sensitive while
       long options are matched case insensitive. To have the single-character options matched
       case insensitive as well, use:

           Getopt::Long::Configure ("bundling", "ignorecase_always");

       It goes without saying that bundling can be quite confusing.

   The lonesome dash
       Normally, a lone dash "-" on the command line will not be considered an option. Option
       processing will terminate (unless "permute" is configured) and the dash will be left in

       It is possible to get special treatment for a lone dash. This can be achieved by adding an
       option specification with an empty name, for example:

           GetOptions ('' => \$stdio);

       A lone dash on the command line will now be a legal option, and using it will set variable

   Argument callback
       A special option 'name' "<>" can be used to designate a subroutine to handle non-option
       arguments. When GetOptions() encounters an argument that does not look like an option, it
       will immediately call this subroutine and passes it one parameter: the argument name.
       Well, actually it is an object that stringifies to the argument name.

       For example:

           my $width = 80;
           sub process { ... }
           GetOptions ('width=i' => \$width, '<>' => \&process);

       When applied to the following command line:

           arg1 --width=72 arg2 --width=60 arg3

       This will call "process("arg1")" while $width is 80, "process("arg2")" while $width is 72,
       and "process("arg3")" while $width is 60.

       This feature requires configuration option permute, see section "Configuring

Configuring Getopt::Long

       Getopt::Long can be configured by calling subroutine Getopt::Long::Configure(). This
       subroutine takes a list of quoted strings, each specifying a configuration option to be
       enabled, e.g.  "ignore_case", or disabled, e.g. "no_ignore_case". Case does not matter.
       Multiple calls to Configure() are possible.

       Alternatively, as of version 2.24, the configuration options may be passed together with
       the "use" statement:

           use Getopt::Long qw(:config no_ignore_case bundling);

       The following options are available:

       default     This option causes all configuration options to be reset to their default

                   This option causes all configuration options to be reset to their default
                   values as if the environment variable POSIXLY_CORRECT had been set.

       auto_abbrev Allow option names to be abbreviated to uniqueness.  Default is enabled unless
                   environment variable POSIXLY_CORRECT has been set, in which case "auto_abbrev"
                   is disabled.

                   Allow "+" to start options.  Default is enabled unless environment variable
                   POSIXLY_CORRECT has been set, in which case "getopt_compat" is disabled.

       gnu_compat  "gnu_compat" controls whether "--opt=" is allowed, and what it should do.
                   Without "gnu_compat", "--opt=" gives an error. With "gnu_compat", "--opt="
                   will give option "opt" and empty value.  This is the way GNU getopt_long()
                   does it.

                   Note that "--opt value" is still accepted, even though GNU getopt_long()

       gnu_getopt  This is a short way of setting "gnu_compat" "bundling" "permute"
                   "no_getopt_compat". With "gnu_getopt", command line handling should be
                   reasonably compatible with GNU getopt_long().

                   Whether command line arguments are allowed to be mixed with options.  Default
                   is disabled unless environment variable POSIXLY_CORRECT has been set, in which
                   case "require_order" is enabled.

                   See also "permute", which is the opposite of "require_order".

       permute     Whether command line arguments are allowed to be mixed with options.  Default
                   is enabled unless environment variable POSIXLY_CORRECT has been set, in which
                   case "permute" is disabled.  Note that "permute" is the opposite of

                   If "permute" is enabled, this means that

                       --foo arg1 --bar arg2 arg3

                   is equivalent to

                       --foo --bar arg1 arg2 arg3

                   If an argument callback routine is specified, @ARGV will always be empty upon
                   successful return of GetOptions() since all options have been processed. The
                   only exception is when "--" is used:

                       --foo arg1 --bar arg2 -- arg3

                   This will call the callback routine for arg1 and arg2, and then terminate
                   GetOptions() leaving "arg3" in @ARGV.

                   If "require_order" is enabled, options processing terminates when the first
                   non-option is encountered.

                       --foo arg1 --bar arg2 arg3

                   is equivalent to

                       --foo -- arg1 --bar arg2 arg3

                   If "pass_through" is also enabled, options processing will terminate at the
                   first unrecognized option, or non-option, whichever comes first.

       bundling (default: disabled)
                   Enabling this option will allow single-character options to be bundled. To
                   distinguish bundles from long option names, long options must be introduced
                   with "--" and bundles with "-".

                   Note that, if you have options "a", "l" and "all", and auto_abbrev enabled,
                   possible arguments and option settings are:

                       using argument               sets option(s)
                       -a, --a                      a
                       -l, --l                      l
                       -al, -la, -ala, -all,...     a, l
                       --al, --all                  all

                   The surprising part is that "--a" sets option "a" (due to auto completion),
                   not "all".

                   Note: disabling "bundling" also disables "bundling_override".

       bundling_override (default: disabled)
                   If "bundling_override" is enabled, bundling is enabled as with "bundling" but
                   now long option names override option bundles.

                   Note: disabling "bundling_override" also disables "bundling".

                   Note: Using option bundling can easily lead to unexpected results, especially
                   when mixing long options and bundles. Caveat emptor.

       ignore_case  (default: enabled)
                   If enabled, case is ignored when matching option names. If, however, bundling
                   is enabled as well, single character options will be treated case-sensitive.

                   With "ignore_case", option specifications for options that only differ in
                   case, e.g., "foo" and "Foo", will be flagged as duplicates.

                   Note: disabling "ignore_case" also disables "ignore_case_always".

       ignore_case_always (default: disabled)
                   When bundling is in effect, case is ignored on single-character options also.

                   Note: disabling "ignore_case_always" also disables "ignore_case".

       auto_version (default:disabled)
                   Automatically provide support for the --version option if the application did
                   not specify a handler for this option itself.

                   Getopt::Long will provide a standard version message that includes the program
                   name, its version (if $main::VERSION is defined), and the versions of
                   Getopt::Long and Perl. The message will be written to standard output and
                   processing will terminate.

                   "auto_version" will be enabled if the calling program explicitly specified a
                   version number higher than 2.32 in the "use" or "require" statement.

       auto_help (default:disabled)
                   Automatically provide support for the --help and -? options if the application
                   did not specify a handler for this option itself.

                   Getopt::Long will provide a help message using module Pod::Usage. The message,
                   derived from the SYNOPSIS POD section, will be written to standard output and
                   processing will terminate.

                   "auto_help" will be enabled if the calling program explicitly specified a
                   version number higher than 2.32 in the "use" or "require" statement.

       pass_through (default: disabled)
                   With "pass_through" anything that is unknown, ambiguous or supplied with an
                   invalid option will not be flagged as an error. Instead the unknown option(s)
                   will be passed to the catchall "<>" if present, otherwise through to @ARGV.
                   This makes it possible to write wrapper scripts that process only part of the
                   user supplied command line arguments, and pass the remaining options to some
                   other program.

                   If "require_order" is enabled, options processing will terminate at the first
                   unrecognized option, or non-option, whichever comes first and all remaining
                   arguments are passed to @ARGV instead of the catchall "<>" if present.
                   However, if "permute" is enabled instead, results can become confusing.

                   Note that the options terminator (default "--"), if present, will also be
                   passed through in @ARGV.

       prefix      The string that starts options. If a constant string is not sufficient, see

                   A Perl pattern that identifies the strings that introduce options.  Default is
                   "--|-|\+" unless environment variable POSIXLY_CORRECT has been set, in which
                   case it is "--|-".

                   A Perl pattern that allows the disambiguation of long and short prefixes.
                   Default is "--".

                   Typically you only need to set this if you are using nonstandard prefixes and
                   want some or all of them to have the same semantics as '--' does under normal

                   For example, setting prefix_pattern to "--|-|\+|\/" and long_prefix_pattern to
                   "--|\/" would add Win32 style argument handling.

       debug (default: disabled)
                   Enable debugging output.

Exportable Methods

           This subroutine provides a standard version message. Its argument can be:

           ·   A string containing the text of a message to print before printing the standard

           ·   A numeric value corresponding to the desired exit status.

           ·   A reference to a hash.

           If more than one argument is given then the entire argument list is assumed to be a
           hash.  If a hash is supplied (either as a reference or as a list) it should contain
           one or more elements with the following keys:

               The text of a message to print immediately prior to printing the program's usage

               The desired exit status to pass to the exit() function.  This should be an
               integer, or else the string "NOEXIT" to indicate that control should simply be
               returned without terminating the invoking process.

               A reference to a filehandle, or the pathname of a file to which the usage message
               should be written. The default is "\*STDERR" unless the exit value is less than 2
               (in which case the default is "\*STDOUT").

           You cannot tie this routine directly to an option, e.g.:

               GetOptions("version" => \&VersionMessage);

           Use this instead:

               GetOptions("version" => sub { VersionMessage() });

           This subroutine produces a standard help message, derived from the program's POD
           section SYNOPSIS using Pod::Usage. It takes the same arguments as VersionMessage(). In
           particular, you cannot tie it directly to an option, e.g.:

               GetOptions("help" => \&HelpMessage);

           Use this instead:

               GetOptions("help" => sub { HelpMessage() });

Return values and Errors

       Configuration errors and errors in the option definitions are signalled using die() and
       will terminate the calling program unless the call to Getopt::Long::GetOptions() was
       embedded in "eval { ...  }", or die() was trapped using $SIG{__DIE__}.

       GetOptions returns true to indicate success.  It returns false when the function detected
       one or more errors during option parsing. These errors are signalled using warn() and can
       be trapped with $SIG{__WARN__}.


       The earliest development of "" started in 1990, with Perl version 4. As a
       result, its development, and the development of Getopt::Long, has gone through several
       stages. Since backward compatibility has always been extremely important, the current
       version of Getopt::Long still supports a lot of constructs that nowadays are no longer
       necessary or otherwise unwanted. This section describes briefly some of these 'features'.

   Default destinations
       When no destination is specified for an option, GetOptions will store the resultant value
       in a global variable named "opt_"XXX, where XXX is the primary name of this option. When a
       program executes under "use strict" (recommended), these variables must be pre-declared
       with our() or "use vars".

           our $opt_length = 0;
           GetOptions ('length=i');    # will store in $opt_length

       To yield a usable Perl variable, characters that are not part of the syntax for variables
       are translated to underscores. For example, "--fpp-struct-return" will set the variable
       $opt_fpp_struct_return. Note that this variable resides in the namespace of the calling
       program, not necessarily "main". For example:

           GetOptions ("size=i", "sizes=i@");

       with command line "-size 10 -sizes 24 -sizes 48" will perform the equivalent of the

           $opt_size = 10;
           @opt_sizes = (24, 48);

   Alternative option starters
       A string of alternative option starter characters may be passed as the first argument (or
       the first argument after a leading hash reference argument).

           my $len = 0;
           GetOptions ('/', 'length=i' => $len);

       Now the command line may look like:

           /length 24 -- arg

       Note that to terminate options processing still requires a double dash "--".

       GetOptions() will not interpret a leading "<>" as option starters if the next argument is
       a reference. To force "<" and ">" as option starters, use "><". Confusing? Well, using a
       starter argument is strongly deprecated anyway.

   Configuration variables
       Previous versions of Getopt::Long used variables for the purpose of configuring. Although
       manipulating these variables still work, it is strongly encouraged to use the "Configure"
       routine that was introduced in version 2.17. Besides, it is much easier.

Tips and Techniques

   Pushing multiple values in a hash option
       Sometimes you want to combine the best of hashes and arrays. For example, the command

         --list add=first --list add=second --list add=third

       where each successive 'list add' option will push the value of add into array ref
       $list->{'add'}. The result would be like

         $list->{add} = [qw(first second third)];

       This can be accomplished with a destination routine:

         GetOptions('list=s%' =>
                      sub { push(@{$list{$_[1]}}, $_[2]) });


   GetOptions does not return a false result when an option is not supplied
       That's why they're called 'options'.

   GetOptions does not split the command line correctly
       The command line is not split by GetOptions, but by the command line interpreter (CLI). On
       Unix, this is the shell. On Windows, it is COMMAND.COM or CMD.EXE. Other operating systems
       have other CLIs.

       It is important to know that these CLIs may behave different when the command line
       contains special characters, in particular quotes or backslashes. For example, with Unix
       shells you can use single quotes ("'") and double quotes (""") to group words together.
       The following alternatives are equivalent on Unix:

           "two words"
           'two words'
           two\ words

       In case of doubt, insert the following statement in front of your Perl program:

           print STDERR (join("|",@ARGV),"\n");

       to verify how your CLI passes the arguments to the program.

   Undefined subroutine &main::GetOptions called
       Are you running Windows, and did you write

           use GetOpt::Long;

       (note the capital 'O')?

   How do I put a "-?" option into a Getopt::Long?
       You can only obtain this using an alias, and Getopt::Long of at least version 2.13.

           use Getopt::Long;
           GetOptions ("help|?");    # -help and -? will both set $opt_help

       Other characters that can't appear in Perl identifiers are also supported as aliases with
       Getopt::Long of at least version 2.39.

       As of version 2.32 Getopt::Long provides auto-help, a quick and easy way to add the
       options --help and -? to your program, and handle them.

       See "auto_help" in section "Configuring Getopt::Long".


       Johan Vromans <>


       This program is Copyright 1990,2015 by Johan Vromans.  This program is free software; you
       can redistribute it and/or modify it under the terms of the Perl Artistic License or the
       GNU General Public License as published by the Free Software Foundation; either version 2
       of the License, or (at your option) any later version.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
       without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       See the GNU General Public License for more details.

       If you do not have a copy of the GNU General Public License write to the Free Software
       Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.