Getopt::Long(3perl)

📦
version 5.44.0 · 14 versions
, in arch rolling

🎀 NAME 🎀

Getopt::Long - Extended processing of command line options

✨ SYNOPSIS ✨

Okay bestie, look at this gorgeous little snippet first:

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");

That's the whole vibe. You hand GetOptions() a list of option specifications and destinations, it does the parsing, you get your variables filled in. Chef's kiss. 💅

💖 DESCRIPTION 💖

So here's the tea: the Getopt::Long module implements an extended getopt function called GetOptions(). What does it do? It parses the command line from @ARGV, recognizing and removing specified options and their possible values. Like, it eats the options for you and leaves the leftovers behind in @ARGV.

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 default. iykyk.

🌈 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', bestie, it's literally optional ✨) but are used to modify its default behaviour.

Like, a program could do its job quietly, but with a suitable option it could provide verbose information about what it did. That's the whole point.

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:

-lac

Options can have values, and 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

or

--size 24
⚠️ The + form is now obsolete and strongly deprecated. Do not be doing that. It's giving 1993. 💀

🦋 Getting Started with Getopt::Long 🦋

Getopt::Long is the Perl5 successor of "newgetopt.pl". 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. Iconic honestly. 👑

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

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 functions — lazy loading, main character energy, we love efficiency.

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. (More on that later, bestie, we're getting there. 🫶)

🌸 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. The duality. The range. 🤌

(If both --verbose and --noverbose are given, whichever is given last takes precedence.)

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. -vvv but make it long and fancy. 🔥

🧚 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 line:

--size 24 -- --all

In this example, --all will not be treated as an option, but passed to the program unharmed, in @ARGV. She's protected. 🛡️✨

🍓 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:

  1. integer numbers,
  2. floating point numbers,
  3. 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.

(If the same option appears more than once on the command line, the last given value is used. If you want to take all the values, see below. 👀)

💅 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 option:

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

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

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

Used with the example above, @libfiles c.q. @$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 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 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 💖

Okay bestie, this is the ultimate power move. If you want full control over what happens when (well, technically: each time) an option shows up on the command line, you can just hand Getopt::Long a reference to a subroutine (or a sneaky anonymous sub) as the option destination. And then? When GetOptions() bumps into that option, it calls your sub with two or three arguments, and it's your moment 💅

  • argument numero uno: the name of the option. (And actually, it's an object that stringifies to the name of the option. cute, right?)
  • if the destination is a scalar or array: the second argument is the value to be stored.
  • if the destination is a hash: the second argument is the key to the hash, and the third argument is the value to be stored.

Then it's fully up to your sub to store the value, or do literally whatever it thinks is appropriate. main character energy fr fr.

A super trivial lil application of this whole mechanism: implementing options that are related to each other. Like, watch this:

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

Here --verbose and --quiet are both controlling the same variable $verbose, but with opposite values. Obsessed with the symmetry. ✨

Now, if your subroutine needs to signal an error, it should call die() with the error message you want as its argument. GetOptions() will catch that die(), throw out the error message, and record that an error result must be returned once it's all done.

But wait 🫶 if the text of the error message starts with an exclamation mark "!", Getopt::Long interprets it specially. There is currently one special command implemented: die("!FINISH") will make GetOptions() stop processing options, just like it hit a double dash --.

Here's an example of how to access the option name and the value from inside a subroutine, iykyk:

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 🌸

Giving your users alternate mnemonic names for options is often the user-friendly thing to do. Like, --height could totally be an alternate name for --length. Bestie behavior 🎀

You include these alternate names right in the option specification, separated by vertical bar "|" characters. To implement the example above:

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

The first name is called the primary name, and all the other names are called aliases. And ngl, when you're using a hash to store options, the key will always be the primary name. No cap.

Multiple alternate names? Absolutely possible. Slay.

🦋 Case and abbreviations 🦋

Without any extra configuration, GetOptions() will straight up ignore the case of option names, and it will allow options to be abbreviated as long as it's unambiguous (to uniqueness, bestie).

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

This call will allow --l and --L for the length option, but it requires at least --hea and --hei for the head and height options. Respect the uniqueness rule or it's over for you 💀

👑 Summary of Option Specifications 👑

Every option specifier is made of two parts: the name specification and the argument specification. Two parts. That's the whole vibe.

The name specification has the name of the option, optionally followed by a list of alternative names separated by vertical bar characters. The name is made up of alphanumeric characters, hyphens, underscores. And heads up: if "pass_through" is disabled, a period is also allowed in option names. ✨

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

The argument specification is optional. If you omit it, the option is considered boolean, and a value of 1 will be assigned when the option is used on the command line. Simple as.

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.
Real talk: using negation on a single letter option when bundling is in effect is pointless and will result in a warning. Just don't 🙈
  • + — 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.
Careful bestie: 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.

If the number is octal, hexadecimal or binary, behaves like ":o".

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

✨ Advanced Possibilities ✨

okay bestie, this is where Getopt::Long stops being a cute little option parser and starts being the whole personality 💅 buckle up.

🧸 Object oriented interface

See Getopt::Long::Parser. that's it, that's the section. iconic, honestly 🫶

🎀 Callback object

so in version 2.37 the first argument to the callback function got changed from a string to an object. why? to make room for extensions and more detailed control. the object stringifies to the option name, so this change should not introduce compatibility problems. slay.

the callback object has these methods:

  • name — the name of the option, unabbreviated. for an option with multiple names it returns the first (canonical) name.
  • given — the name of the option as actually used, unabbreviated.

🧵 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. periodt. don't use the old one, bestie, it's giving deprecated 💀

📖 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;

__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. no cap, it's a whole vibe 🌸

📦 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, and the global @ARGV is not touched at all. so respectful 🫶

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 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, the global @ARGV is not touched.

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. so if you're in scalar land and there's leftovers, it's gonna be dramatic 😭

as with GetOptionsFromArray, a first argument hash reference now becomes the second argument. see the next section.

🗂️ 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. in 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 ... }

🎁 Bundling

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

-vax

will set all three. it's giving combo meal 🍟

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 (and any of their auto-abbreviated shortened forms) must always start with a double dash -- to avoid ambiguity. for example, when vax, a, v and x are all valid options,

-vax

will set a, v and x, but

--vax

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. wild, I know.

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

-h24w80

is equivalent to

-h 24 -w 80

a third style of bundling allows only values to be bundled with options. it can be enabled with:

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. not cute, don't do it 💅

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. fr fr, it's a lot.

➖ 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 @ARGV.

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 $stdio. main character energy for one little dash ✨

🫂 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.

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. so it's processing in real time, bestie 🦋

this feature requires configuration option permute, see section "Configuring Getopt::Long".

✨ Configuring Getopt::Long ✨

okay so bestie, you can tune Getopt::Long to your exact vibe 💅 — just call the subroutine Getopt::Long::Configure(). Hand it a list of quoted strings, each one naming a config option you wanna turn on, like "ignore_case". Wanna turn one off? Just prefix it with "no" or "no_", like "no_ignore_case". Capitalization? Doesn't matter. And yes, you can call Configure() as many times as you want. Live your life.

Alternatively — and this has been a thing since version 2.24 — you can pass the config options right along with the use statement:

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

Here's the whole menu of config options available:

  • default — resets every config option back to its default value. Factory reset energy.
  • posix_default — resets every config option back to its default value, but as if the environment variable POSIXLY_CORRECT had been set.
  • auto_abbrev — lets option names be abbreviated, as long as the abbreviation is unique enough to nail it down. Default is enabled, unless the environment variable POSIXLY_CORRECT has been set — in which case auto_abbrev is disabled.
  • getopt_compat — allows "+" to start options. Default is enabled, unless the environment variable POSIXLY_CORRECT has been set, in which case getopt_compat is disabled.
  • gnu_compat — controls whether --opt= is allowed and what it does. Without gnu_compat, --opt= throws an error. With gnu_compat, --opt= hands option opt an empty value. This is exactly how GNU getopt_long() does it. 🫶

Heads up tho: for options with optional arguments, --opt value is still accepted, even though GNU getopt_long() requires you to write --opt=value in that case.

  • gnu_getopt — this is the shortcut bundle ✨ it's a short way of setting gnu_compat, bundling, permute, and no_getopt_compat all at once. With gnu_getopt, your command line handling should be reasonably compatible with GNU getopt_long().
  • require_order — whether command line arguments are allowed to be mixed in with options. Default is disabled, unless the environment variable POSIXLY_CORRECT has been set, in which case require_order is enabled.

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

  • permute — whether command line arguments are allowed to be mixed in with options. Default is enabled, unless the environment variable POSIXLY_CORRECT has been set, in which case permute is disabled. And reminder: permute is the opposite of require_order.

If permute is enabled, that means:

--foo arg1 --bar arg2 arg3

hits the same as:

--foo --bar arg1 arg2 arg3

If an argument callback routine is specified, @ARGV will always be empty once GetOptions() returns successfully, since all the options got processed. The only exception is when -- shows up:

--foo arg1 --bar arg2 -- arg3

This calls the callback routine for arg1 and arg2, then terminates GetOptions() while leaving arg3 sitting in @ARGV. 💀

If require_order is enabled, options processing stops the moment the first non-option appears.

--foo arg1 --bar arg2 arg3

is equivalent to:

--foo -- arg1 --bar arg2 arg3

And if pass_through is also enabled, options processing will terminate at the first unrecognized option, or the first non-option — whichever one comes first.

  • bundling (default: disabled) — enabling this lets single-character options get bundled together. So to tell bundles apart from long option names, long options (and any of their auto-abbreviated shortened forms) must be introduced with --, while bundles use -.

Watch this: if you've got options a, l and all, and auto_abbrev is enabled, here are the possible arguments and option settings:

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

The plot twist that gets everybody? --a sets option a (thanks to auto completion), not all. 😭

Note: disabling bundling also disables bundling_override.

  • bundling_override (default: disabled) — if this is enabled, bundling is enabled just like 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 you're mixing long options and bundles. Caveat emptor. 🙈
  • ignore_case (default: enabled) — if enabled, case gets ignored when matching option names. But if bundling is enabled too, single character options are treated case-sensitive.

With ignore_case, option specifications for options that only differ in case — like 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, this makes case get ignored on single-character options too.

Note: disabling ignore_case_always also disables ignore_case.

  • auto_version (default:disabled) — automatically provides support for the --version option if the application didn't specify a handler for it itself.

Getopt::Long will hand you a standard version message that includes the program name, its version (if $main::VERSION is defined), and the versions of Getopt::Long and Perl. That message gets written to standard output and processing terminates. slay. ✨

auto_version gets 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 provides support for the --help and -? options if the application didn't specify a handler for this option itself.

Getopt::Long will produce a help message using the module Pod::Usage. The message, derived from the SYNOPSIS POD section, gets written to standard output and processing terminates. 🥹 so helpful

auto_help gets 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 unknown, ambiguous, or supplied with an invalid option will not be flagged as an error. Instead the unknown option(s) get passed to the catchall <> if it's present, otherwise through to @ARGV. This makes it possible to write wrapper scripts that only process part of the user-supplied command line arguments and hand the remaining options off to some other program. iconic behavior honestly.

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

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

  • prefix — the string that starts options. If a constant string isn't enough for you, go look at prefix_pattern.
  • prefix_pattern — a Perl pattern that identifies the strings that introduce options. Default is --|-|\+ unless the environment variable POSIXLY_CORRECT has been set, in which case it's --|-.
  • long_prefix_pattern — a Perl pattern that allows the disambiguation of long and short prefixes. Default is --.

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

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 💖

🦋 VersionMessage

okay so this subroutine hands you a standard version message, no cap. its argument can be:

  • a string containing the text of a message to print before printing the 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 is assumed to be a hash. and if a hash is supplied (either as a reference or as a list, we don't judge) it should contain one or more elements with these keys, bestie:

  • -message, -msg — the text of a message to print immediately prior to printing the program's usage message 💬
  • -exitval — 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 🫶
  • -output — 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) ✨
🚨 and listen — you cannot tie this routine directly to an option, like: GetOptions("version" => \&VersionMessage); nope. use this instead: GetOptions("version" => sub { VersionMessage() });

🎀 HelpMessage

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(). and same deal as before — in particular, you cannot tie it directly to an option, like:

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

use this instead, bestie:

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__}. so like, heads up 💀

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__}.

💜 Legacy 💜

the earliest development of newgetopt.pl started in 1990, with Perl version 4. wild, right? 🦕 as a result, its development — and the development of Getopt::Long — has gone through several stages. and 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 (which is recommended, fr fr), these variables must be pre-declared with our().

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 assignments

$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 --, no exceptions bestie.

GetOptions() will not interpret a leading <> as option starters if the next argument is a reference. to force < and > as option starters, use ><. confusing? yeah honestly 😭 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 💅 periodt.

🌸 Tips and Techniques 🌸

🍓 Pushing multiple values in a hash option

sometimes you want to combine the best of hashes and arrays, main character energy only. for example, the command line:

--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]) });

slay 💖

🙈 Troubleshooting 🙈

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 in aliases with Getopt::Long of at version 2.39. note that the characters !, |, +, =, and : can only appear as the first (or only) character of an alias ✨

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.

👑 AUTHOR 👑

Johan Vromans <jvromans@squirrel.nl>

this program is Copyright 1990,2015,2023 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.

and that's a wrap on the whole page bestie 🎀 this one's from perl v5.44.0, dated 2026-10-17, filed under Getopt::Long(3perl) — literally iconic, go get those command line options 💖✨

📦 where this page comes from