Getopt::Long(3perl) Perl Programmers Reference Guide Getopt::Long(3perl)
NAME
Getopt::Long - Extended processing of command line options
SYNOPSIS
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");
DESCRIPTION
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
default.
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:
-lac
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
or
--size 24
The "+" form is now obsolete and strongly deprecated.
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.
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.
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".
(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.
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.
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 $tag = ''; # option variable with default value
GetOptions ('tag=s' => \$tag);
In the option specification, the option name is followed by an equals
sign "=" and the letter "s". The equals sign indicates that this option
requires a value. The letter "s" indicates that this value is an
arbitrary string. Other possible value types are "i" for integer values,
and "f" for floating point values. Using a colon ":" instead of the
equals sign indicates that the option value is optional. In this case,
if no suitable value is supplied, string valued options get an empty
string '' assigned, while numeric options are set to 0.
(If the same option appears more than once on the command line, the last
given value is used. If you want to take all the values, see below.)
Options with multiple values
Options sometimes take several values. For example, a program could use
multiple directories to search for library files:
--library lib/stdlib --library lib/extlib
To accomplish this behaviour, simply specify an array reference as the
destination for the option:
GetOptions ("library=s" => \@libfiles);
Alternatively, you can specify that the option can have multiple values
by adding a "@", and pass a reference to a scalar as the destination:
GetOptions ("library=s@" => \$libfiles);
Used with the example above, @libfiles c.q. @$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
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 $verbose, but
with opposite values.
If the subroutine needs to signal an error, it should call die() with
the desired error message as its argument. GetOptions() will catch the
die(), issue the error message, and record that an error result must be
returned upon completion.
If the text of the error message starts with an exclamation mark "!" it
is interpreted specially by GetOptions(). There is currently one special
command implemented: die("!FINISH") will cause GetOptions() to stop
processing options, as if it encountered a double dash "--".
Here is an example of how to access the option name and value from
within a subroutine:
GetOptions ('opt=i' => \&handler);
sub handler {
my ($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
example:
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 specification.
The name specification contains 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. 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 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.
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
Object oriented interface
See Getopt::Long::Parser.
Callback object
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.
The callback object has the following methods:
name
The name of the option, unabbreviated. For an option with multiple
names it return the first (canonical) name.
given
The name of the option as actually used, unabbreveated.
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;
__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 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 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.
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, 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 ... }
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.
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".
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.
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 @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.
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.
This feature requires configuration option permute, see section
"Configuring Getopt::Long".
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". To disable, prefix with "no" or "no_", 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 values.
posix_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.
getopt_compat
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" an empty
value. This is the way GNU getopt_long() does it.
Note that for options with optional arguments, "--opt value"
is still accepted, even though GNU getopt_long() requires
writing "--opt=value" in this case.
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().
require_order
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
"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 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 (and any of their auto-abbreviated shortened
forms) 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 "prefix_pattern".
prefix_pattern
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 "--|-".
long_prefix_pattern
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 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
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 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. If a hash is supplied (either as a reference
or as a list) it should contain one or more elements with the
following keys:
"-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").
You cannot tie this routine directly to an option, e.g.:
GetOptions("version" => \&VersionMessage);
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(). 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__}.
Legacy
The earliest development of "newgetopt.pl" 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().
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
"--".
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 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]) });
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>
COPYRIGHT AND DISCLAIMER
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.
perl v5.40.1 2026-08-30 Getopt::Long(3perl)
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