Getopt::Long(3p)Perl Programmers Reference Guide Getopt::Long(3p)
Getopt::Long - Extended processing of command line options
use Getopt::Long;
my $data = "file.dat";
my $length = 24;
my $verbose;
$result = GetOptions ("length=i" => \$length, # numeric
"file=s" => \$data, # string
"verbose" => \$verbose); # flag
The Getopt::Long module implements an extended getopt func-
tion called GetOptions(). 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 informa-
tion 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
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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, hence the name
Getopt::Long. This module also supports single-character
options and bundling. Single character options may be any
alphabetic character, a question mark, and a dash. Long
options may consist of a series of letters, digits, and
dashes. Although this is currently not enforced by
Getopt::Long, multiple consecutive dashes are not allowed,
and the option name must not end with a dash.
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 abbrevi-
ated 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:
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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 destina-
tion.
GetOptions() will return a true value if the command line
could be processed successfully. Otherwise, it will write
error messages to STDERR, 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 $ver-
bose, as expected. But it is also allowed to use "--nover-
bose", which will disable $verbose by setting its value to
0. Using a suitable default value, the program can find out
whether $verbose is false by default, or disabled by using
"--noverbose".
An incremental option is specified with a plus "+" after the
option name:
my $verbose = ''; # option variable with default value (false)
GetOptions ('verbose+' => \$verbose);
Using "--verbose" on the command line will increment the
value of $verbose. This way the program can keep track of
how many times the option occurred on the command line. For
example, each occurrence of "--verbose" could increase the
verbosity level of the program.
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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, float-
ing 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 $tag = ''; # option variable with default value
GetOptions ('tag=s' => \$tag);
In the option specification, the option name is followed by
an equals sign "=" and the letter "s". The equals sign indi-
cates that this option requires a value. The letter "s"
indicates that this value is an arbitrary string. Other pos-
sible value types are "i" for integer values, and "f" for
floating point values. Using a colon ":" instead of the
equals sign indicates that the option value is optional. In
this case, if no suitable value is supplied, string valued
options get an empty string '' assigned, while numeric
options are set to 0.
Options with multiple values
Options sometimes take several values. For example, a pro-
gram could use multiple directories to search for library
files:
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--library lib/stdlib --library lib/extlib
To accomplish this behaviour, simply specify an array refer-
ence as the destination for the option:
GetOptions ("library=s" => \@libfiles);
Alternatively, you can specify that the option can have mul-
tiple values by adding a "@", and pass a scalar reference as
the destination:
GetOptions ("library=s@" => \$libfiles);
Used with the example above, @libfiles (or @$libfiles) would
contain two strings upon completion: "lib/srdlib" 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{,}" indicates one or more values; "foo:s{,}" indi-
cates zero or more option values.
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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 subrou-
tine with two or three arguments. The first argument is the
name of the option. For a scalar or array destination, the
second argument is the value to be stored. For a hash desti-
nation, the second arguments is the key to the hash, and the
third argument the value to be stored. It is up to the sub-
routine 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. GetOp-
tions() will catch the die(), issue the error message, and
record that an error result must be returned upon comple-
tion.
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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 "--".
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 "|" charac-
ters. 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 abbre-
viated 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.
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
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! 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 incre-
mented 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. Sup-
ported 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 hexa-
decimal 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 other-
wise 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 "=" / ":" seman-
tics.
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max denotes the maximum number of arguments. It must be
at least min. If max is omitted, but the comma is not,
there is no upper bound to the number of argument values
taken.
: type [ desttype ]
Like "=", but designates the argument as optional. If
omitted, an empty string will be assigned to string
values options, and the value zero to numeric options.
Note that if a string argument starts with "-" or "--",
it will be considered an option on itself.
: number [ desttype ]
Like ":i", but if the value is omitted, the number will
be assigned.
: + [ desttype ]
Like ":i", but if the value is omitted, the current
value for the option will be incremented.
Object oriented interface
Getopt::Long can be used in an object oriented way as well:
use Getopt::Long;
$p = new Getopt::Long::Parser;
$p->configure(...configuration options...);
if ($p->getoptions(...options descriptions...)) ...
Configuration options can be passed to the constructor:
$p = new Getopt::Long::Parser
config => [...configuration options...];
Thread Safety
Getopt::Long is thread safe when using ithreads as of Perl
5.8. It is not thread safe when using the older (experimen-
tal 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;
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my $man = 0;
my $help = 0;
GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
pod2usage(1) if $help;
pod2usage(-exitstatus => 0, -verbose => 2) if $man;
__END__
=head1 NAME
sample - Using Getopt::Long and Pod::Usage
=head1 SYNOPSIS
sample [options] [file ...]
Options:
-help brief help message
-man full documentation
=head1 OPTIONS
=over 8
=item B<-help>
Print a brief help message and exits.
=item B<-man>
Prints the manual page and exits.
=back
=head1 DESCRIPTION
B<This program> will read the given input file(s) and do something
useful with the contents thereof.
=cut
See Pod::Usage for details.
Storing option values in a hash
Sometimes, for example when there are a lot of options, hav-
ing a separate variable for each of them can be cumbersome.
GetOptions() supports, as an alternative mechanism, storing
options in a hash.
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To obtain this, a reference to a hash must be passed as the
first argument to GetOptions(). For each option that is
specified on the command line, the option value will be
stored in the hash with the option name as key. Options that
are not actually used on the command line will not be put in
the hash, on other words, "exists($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 refer-
ences 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
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would set all three.
Getopt::Long supports two levels of bundling. To enable bun-
dling, a call to Getopt::Long::Configure is required.
The first level of bundling can be enabled with:
Getopt::Long::Configure ("bundling");
Configured this way, single-character options can be bundled
but long options must always start with a double dash "--"
to avoid ambiguity. For example, when "vax", "a", "v" and
"x" are all valid options,
-vax
would set "a", "v" and "x", but
--vax
would set "vax".
The second level of bundling lifts this restriction. It can
be enabled with:
Getopt::Long::Configure ("bundling_override");
Now, "-vax" would set the option "vax".
When any level of bundling is enabled, option values may be
inserted in the bundle. For example:
-h24w80
is equivalent to
-h 24 -w 80
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
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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 sub-
routine 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 sec-
tion "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", or disabled, e.g.
"no_ignore_case". Case does not matter. Multiple calls to
Configure() are possible.
Alternatively, as of version 2.24, the configuration options
may be passed together with the "use" statement:
use Getopt::Long qw(:config no_ignore_case bundling);
The following options are available:
default This option causes all configuration options to
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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 unique-
ness. 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 dis-
abled.
gnu_compat "gnu_compat" controls whether "--opt=" is
allowed, and what it should do. Without
"gnu_compat", "--opt=" gives an error. With
"gnu_compat", "--opt=" will give option "opt"
and empty value. This is the way GNU
getopt_long() does it.
gnu_getopt This is a short way of setting "gnu_compat"
"bundling" "permute" "no_getopt_compat". With
"gnu_getopt", command line handling should be
fully 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
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--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
"arg2" in @ARGV.
If "require_order" is enabled, options process-
ing 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 pro-
cessing will terminate at the first unrecognized
option, or non-option, whichever comes first.
bundling (default: disabled)
Enabling this option will allow single-character
options to be bundled. To distinguish bundles
from long option names, long options must be
introduced with "--" and bundles with "-".
Note that, if you have options "a", "l" and
"all", and auto_abbrev enabled, possible argu-
ments 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)
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If "bundling_override" is enabled, bundling is
enabled as with "bundling" but now long option
names override option bundles.
Note: disabling "bundling_override" also dis-
ables "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 long
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 dis-
ables "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 ver-
sion (if $main::VERSION is defined), and the
versions of Getopt::Long and Perl. The message
will be written to standard output and process-
ing 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.
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Getopt::Long will provide a help message using
module Pod::Usage. The message, derived from the
SYNOPSIS POD section, will be written to stan-
dard output and processing will terminate.
"auto_help" will be enabled if the calling pro-
gram explicitly specified a version number
higher than 2.32 in the "use" or "require"
statement.
pass_through (default: disabled)
Options that are unknown, ambiguous or supplied
with an invalid option value are passed through
in @ARGV instead of being flagged as errors.
This makes it possible to write wrapper scripts
that process only part of the user supplied com-
mand line arguments, and pass the remaining
options to some other program.
If "require_order" is enabled, options process-
ing will terminate at the first unrecognized
option, or non-option, whichever comes first.
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)
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Getopt::Long(3p)Perl Programmers Reference Guide Getopt::Long(3p)
Enable debugging output.
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 argu-
ment list is assumed to be a hash. If a hash is sup-
plied (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() func-
tion. 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 VersionMes-
sage(). In particular, you cannot tie it directly to an
option, e.g.:
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Getopt::Long(3p)Perl Programmers Reference Guide Getopt::Long(3p)
GetOptions("help" => \&HelpMessage);
Use this instead:
GetOptions("help" => sub { HelpMessage() });
Configuration errors and errors in the option definitions
are signalled using die() and will terminate the calling
program unless the call to Getopt::Long::GetOptions() was
embedded in "eval { ... }", or die() was trapped using
$SIG{__DIE__}.
GetOptions returns true to indicate success. It returns
false when the function detected one or more errors during
option parsing. These errors are signalled using warn() and
can be trapped with $SIG{__WARN__}.
The earliest development of "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 progam executes under "use strict" (recommended),
these variables must be pre-declared with our() or "use
vars".
our $opt_length = 0;
GetOptions ('length=i'); # will store in $opt_length
To yield a usable Perl variable, characters that are not
part of the syntax for variables are translated to under-
scores. 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 neces-
sarily "main". For example:
GetOptions ("size=i", "sizes=i@");
with command line "-size 10 -sizes 24 -sizes 48" will per-
form the equivalent of the assignments
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Getopt::Long(3p)Perl Programmers Reference Guide Getopt::Long(3p)
$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 vari-
ables still work, it is strongly encouraged to use the "Con-
figure" routine that was introduced in version 2.17.
Besides, it is much easier.
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 com-
mand line interpreter (CLI). On Unix, this is the shell. On
Windows, it is COMMAND.COM or CMD.EXE. Other operating sys-
tems have other CLIs.
It is important to know that these CLIs may behave different
when the command line contains special characters, in par-
ticular 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:
perl v5.8.8 2005-02-05 20
Getopt::Long(3p)Perl Programmers Reference Guide Getopt::Long(3p)
"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
Johan Vromans <jvromans@squirrel.nl>
This program is Copyright 1990,2005 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 use-
ful, but WITHOUT ANY WARRANTY; without even the implied war-
ranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR-
POSE. 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 v5.8.8 2005-02-05 21