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Section: User Contributed Perl Documentation (3)
Updated: 2017-05-27


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 calledGetOptions(). It parses the command line from @ARGV, recognizingand removing specified options and their possible values.

This function adheres to the POSIX syntax for commandline options, with GNU extensions. In general, this means that optionshave long names instead of single letters, and are introduced with adouble dash ``--''. Support for bundling of command line options, as wasthe case with the more traditional single-letter approach, is providedbut not enabled by default. 

Command Line Options, an Introduction

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

Command line options come in several flavours. Historically, they arepreceded 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 optioncharacter. Sometimes with whitespace in between, sometimes not:

    -s 24 -s24

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



    --size 24

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

Getting Started with Getopt::Long

Getopt::Long is the Perl5 successor of "". This was thefirst Perl module that provided support for handling the new style ofcommand line options, in particular long option names, hence the Perl5name Getopt::Long. This module also supports single-character optionsand bundling.

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

    use Getopt::Long;

This will load the core of the Getopt::Long module and prepare yourprogram for using it. Most of the actual Getopt::Long code is notloaded until you really call one of its functions.

In the default configuration, options names may be abbreviated touniqueness, case does not matter, and a single dash is sufficient,even for long option names. Also, options may be placed betweennon-option arguments. See ``Configuring Getopt::Long'' for moredetails on how to configure Getopt::Long. 

Simple options

The most simple options are the ones that take no values. Their merepresence 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 arepresent in @ARGV and sets the option variable to the value 1 ifthe option did occur on the command line. Otherwise, the optionvariable is not touched. Setting the option value to true is oftencalled enabling the option.

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

GetOptions() will return a true value if the command line could beprocessed successfully. Otherwise, it will write error messages usingdie() 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 theoption 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 willdisable $verbose by setting its value to 0. Using a suitabledefault value, the program can find out whether $verbose is falseby default, or disabled by using "--noverbose".

An incremental option is specified with a plus "+" after theoption 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 theoption 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 theoptions 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 theprogram. To stop Getopt::Long from processing further arguments,insert a double dash "--" on the command line:

    --size 24 -- --all

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

Options with values

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

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

If the option value is required, Getopt::Long will take thecommand line argument that follows the option and assign this to theoption variable. If, however, the option value is specified asoptional, this will only be done if that value does not look like avalid 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 equalssign "=" and the letter "s". The equals sign indicates that thisoption requires a value. The letter "s" indicates that this value isan arbitrary string. Other possible value types are "i" for integervalues, and "f" for floating point values. Using a colon ":" insteadof the equals sign indicates that the option value is optional. Inthis case, if no suitable value is supplied, string valued options getan empty string '' assigned, while numeric options are set to 0. 

Options with multiple values

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

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

To accomplish this behaviour, simply specify an array reference as thedestination for the option:

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

Alternatively, you can specify that the option can have multiplevalues by adding a ``@'', and pass a reference to a scalar as thedestination:

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

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

Often it is useful to allow comma-separated lists of values as well asmultiple 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 foreach 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 optionspecification. 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 ofarguments an option takes. "foo=s{2,4}" indicates an option thattakes at least two and at most 4 arguments. "foo=s{1,}" indicates oneor 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 willtake, as value, strings of the form key"="value. The value willbe stored with the specified key in the hash.

    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 isalso possible to specify that only integer or floating point numbersare 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 bydesignating a reference to a subroutine (or an anonymous subroutine)as the option destination. When GetOptions() encounters the option, itwill call the subroutine with two or three arguments. The firstargument is the name of the option. (Actually, it is an object thatstringifies 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 argumentthe 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 thatare 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 values.

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

If the text of the error message starts with an exclamation mark "!"it is interpreted specially by GetOptions(). There is currently onespecial 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 waschanged from string to object. This was done to make room forextensions and more detailed control. The object stringifies to theoption name so this change should not introduce compatibilityproblems.

Here is an example of how to access the option name and value from withina 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 foroptions. For example "--height" could be an alternate name for"--length". Alternate names can be included in the optionspecification, separated by vertical bar "|" characters. To implementthe above example:

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

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

Multiple alternate names are possible. 

Case and abbreviations

Without additional configuration, GetOptions() will ignore the case ofoption 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, butrequires a least "--hea" and "--hei" for the head and height options. 

Summary of Option Specifications

Each option specifier consists of two parts: the name specificationand the argument specification.

The name specification contains the name of the option, optionallyfollowed by a list of alternative names separated by vertical barcharacters.

    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 isconsidered boolean, a value of 1 will be assigned when the option isused on the command line.

The argument specification can be

The option does not take an argument and may be negated by prefixingit with ``no'' or ``no-''. E.g. "foo!" will allow "--foo" (a value of1 will be assigned) as well as "--nofoo" and "--no-foo" (a value of0 will be assigned). If the option has aliases, this applies to thealiases as well.

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

The option does not take an argument and will be incremented by 1every time it appears on the command line. E.g. "more+", when usedwith "--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 typesare:
String. An arbitrary sequence of characters. It is valid for theargument to start with "-" or "--".
Integer. An optional leading plus or minus sign, followed by asequence of digits.
Extended integer, Perl style. This can be either an optional leadingplus or minus sign, followed by a sequence of digits, or an octalstring (a zero, optionally followed by '0', '1', .. '7'), or ahexadecimal string ("0x" followed by '0' .. '9', 'a' .. 'f', caseinsensitive), or a binary string ("0b" followed by a series of '0'and '1').
Real number. For example 3.14, "-6.23E24" and so on.

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

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

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

max denotes the maximum number of arguments. It must be at leastmin. If max is omitted, but the comma is not, there is noupper 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 beconsidered 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 theoption will be incremented.

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 isnot thread safe when using the older (experimental and nowobsolete) threads implementation that was added to Perl 5.005. 

Documentation and help texts

Getopt::Long encourages the use of Pod::Usage to produce helpmessages. 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;    __END__    =head1 NAME    sample - Using Getopt::Long and Pod::Usage    =head1 SYNOPSIS    sample [options] [file ...]     Options:       -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.    =back    =head1 DESCRIPTION    B<This program> will read the given input file(s) and do something    useful with the contents thereof.    =cut

See Pod::Usage for details. 

Parsing options from an arbitrary array

By default, GetOptions parses the options that are present in theglobal array @ARGV. A special entry "GetOptionsFromArray" can beused 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 removedfrom @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 thesecond argument:

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

Parsing options from an arbitrary string

A special entry "GetOptionsFromString" can be used to parse optionsfrom an arbitrary string.

    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", theglobal @ARGV is not touched.

It is possible that, upon completion, not all arguments in the stringhave been processed. "GetOptionsFromString" will, when called in listcontext, return both the return status and an array reference to anyremaining arguments:

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

If any arguments remain, and "GetOptionsFromString" was not called inlist context, a message will be given and "GetOptionsFromString" willreturn failure.

As with GetOptionsFromArray, a first argument hash reference nowbecomes the second argument. 

Storing options values in a hash

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

To obtain this, a reference to a hash must be passed as the firstargument to GetOptions(). For each option that is specified on thecommand line, the option value will be stored in the hash with theoption name as key. Options that are not actually used on the commandline will not be put in the hash, on other words,"exists($h{option})" (or defined()) can be used to test if an optionwas used. The drawback is that warnings will be issued if the programruns under "use strict" and uses $h{option} without testing withexists() 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 indicatethis 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 tothe 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 optionscould be stored in variables while all other options get stored in thehash:

    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 optionsat 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, acall 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 longoptions must always start with a double dash "--" to avoidambiguity. For example, when "vax", "a", "v" and "x" are all validoptions,


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


will set "vax".

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

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

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

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


is equivalent to

    -h 24 -w 80

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

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

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

Enabling "bundling_values" will disable the other two styles ofbundling.

When configured for bundling, single-character options are matchedcase sensitive while long options are matched case insensitive. Tohave 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 consideredan option. Option processing will terminate (unless ``permute'' isconfigured) and the dash will be left in @ARGV.

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

    GetOptions ('' => \$stdio);

A lone dash on the command line will now be a legal option, and usingit will set variable $stdio. 

Argument callback

A special option 'name' "<>" can be used to designate a subroutineto handle non-option arguments. When GetOptions() encounters anargument that does not look like an option, it will immediately call thissubroutine and passes it one parameter: the argument name. Well, actuallyit 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 Getopt::Long''. 

Configuring Getopt::Long

Getopt::Long can be configured by calling subroutineGetopt::Long::Configure(). This subroutine takes a list of quotedstrings, each specifying a configuration option to be enabled, e.g."ignore_case", or disabled, e.g. "no_ignore_case". Case does notmatter. Multiple calls to Configure() are possible.

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

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

The following options are available:

This option causes all configuration options to be reset to theirdefault values.
This option causes all configuration options to be reset to theirdefault values as if the environment variable POSIXLY_CORRECT hadbeen set.
Allow option names to be abbreviated to uniqueness.Default is enabled unless environment variablePOSIXLY_CORRECT has been set, in which case "auto_abbrev" is disabled.
Allow "+" to start options.Default is enabled unless environment variablePOSIXLY_CORRECT has been set, in which case "getopt_compat" is disabled.
"gnu_compat" controls whether "--opt=" is allowed, and what it shoulddo. 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 GNUgetopt_long() doesn't.

This is a short way of setting "gnu_compat" "bundling" "permute""no_getopt_compat". With "gnu_getopt", command line handling should bereasonably compatible with GNU getopt_long().
Whether command line arguments are allowed to be mixed with options.Default is disabled unless environment variablePOSIXLY_CORRECT has been set, in which case "require_order" is enabled.

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

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

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 beempty upon successful return of GetOptions() since all options have beenprocessed. The only exception is when "--" is used:

    --foo arg1 --bar arg2 -- arg3

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

If "require_order" is enabled, options processingterminates 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 terminateat the first unrecognized option, or non-option, whichever comesfirst.

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

Note that, if you have options "a", "l" and "all", andauto_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 autocompletion), 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 treatedcase-sensitive.

With "ignore_case", option specifications for options that onlydiffer in case, e.g., "foo" and "Foo", will be flagged asduplicates.

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

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

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

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

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

"auto_version" will be enabled if the calling program explicitlyspecified 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 ifthe application did not specify a handler for this option itself.

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

"auto_help" will be enabled if the calling program explicitlyspecified 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 withan invalid option will not be flagged as an error. Instead the unknownoption(s) will be passed to the catchall "<>" if present, otherwisethrough to @ARGV. This makes it possible to write wrapper scripts thatprocess only part of the user supplied command line arguments, and pass theremaining options to some other program.

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

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

The string that starts options. If a constant string is notsufficient, see "prefix_pattern".
A Perl pattern that identifies the strings that introduce options.Default is "--|-|\+" unless environment variablePOSIXLY_CORRECT has been set, in which case it is "--|-".
A Perl pattern that allows the disambiguation of long and shortprefixes. Default is "--".

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

For example, setting prefix_pattern to "--|-|\+|\/" andlong_prefix_pattern to "--|\/" would add Win32 style argumenthandling.

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 printingthe standard message.
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 isassumed to be a hash. If a hash is supplied (either as a reference oras a list) it should contain one or more elements with the followingkeys:

The text of a message to print immediately prior to printing theprogram's usage message.
The desired exit status to pass to the exit() function.This should be an integer, or else the string ``NOEXIT'' toindicate that control should simply be returned withoutterminating the invoking process.
A reference to a filehandle, or the pathname of a file to which theusage message should be written. The default is "\*STDERR" unless theexit 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 theprogram's POD section SYNOPSIS using Pod::Usage. It takes the samearguments as VersionMessage(). In particular, you cannot tie itdirectly 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 aresignalled using die() and will terminate the calling program unlessthe 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 duringoption parsing. These errors are signalled using warn() and can betrapped with $SIG{__WARN__}. 


The earliest development of "" started in 1990, with Perlversion 4. As a result, its development, and the development ofGetopt::Long, has gone through several stages. Since backwardcompatibility has always been extremely important, the current versionof Getopt::Long still supports a lot of constructs that nowadays areno longer necessary or otherwise unwanted. This section describesbriefly some of these 'features'. 

Default destinations

When no destination is specified for an option, GetOptions will storethe resultant value in a global variable named "opt_"XXX, whereXXX is the primary name of this option. When a program executesunder "use strict" (recommended), these variables must bepre-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 thesyntax 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 thenamespace of the calling program, not necessarily "main". Forexample:

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

with command line ``-size 10 -sizes 24 -sizes 48'' will perform theequivalent of the assignments

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

Alternative option starters

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

    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 startersif the next argument is a reference. To force "<" and ">" asoption starters, use "><". Confusing? Well, using a starterargument is strongly deprecated anyway. 

Configuration variables

Previous versions of Getopt::Long used variables for the purpose ofconfiguring. Although manipulating these variables still work, it isstrongly encouraged to use the "Configure" routine that was introducedin 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. Forexample, the command line:

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

where each successive 'list add' option will push the value of addinto 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 lineinterpreter (CLI). On Unix, this is the shell. On Windows, it isCOMMAND.COM or CMD.EXE. Other operating systems have other CLIs.

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

    "two words"    'two words'    two\ words

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

    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 leastversion 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 supportedas aliases with Getopt::Long of at least version 2.39.

As of version 2.32 Getopt::Long provides auto-help, a quick and easy wayto 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/ormodify it under the terms of the Perl Artistic License or theGNU General Public License as published by the Free SoftwareFoundation; either version 2 of the License, or (at your option) anylater version.

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

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



Command Line Options, an Introduction
Getting Started with Getopt::Long
Simple options
A little bit less simple options
Mixing command line option with other arguments
Options with values
Options with multiple values
Options with hash values
User-defined subroutines to handle options
Options with multiple names
Case and abbreviations
Summary of Option Specifications
Advanced Possibilities
Object oriented interface
Thread Safety
Documentation and help texts
Parsing options from an arbitrary array
Parsing options from an arbitrary string
Storing options values in a hash
The lonesome dash
Argument callback
Configuring Getopt::Long
Exportable Methods
Return values and Errors
Default destinations
Alternative option starters
Configuration variables
Tips and Techniques
Pushing multiple values in a hash option
GetOptions does not return a false result when an option is not supplied
GetOptions does not split the command line correctly
Undefined subroutine &main::GetOptions called
How do I put a -? option into a Getopt::Long?

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