Getopt::Long - Extended processing of command line options
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 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.
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.
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:
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.
Getopt::Long supports two useful variants of simple options: negatable options and incremental options.
A negatable option is specified with an exclamation mark !
after the
option name:
- my $verbose = ''; # option variable with default value (false)
- GetOptions ('verbose!' => \$verbose);
Now, using --verbose
on the command line will enable $verbose
,
as expected. But it is also allowed to use --noverbose
, which will
disable $verbose
by setting its value to 0
. Using a suitable
default value, the program can find out whether $verbose
is false
by default, or disabled by using --noverbose
.
An incremental option is specified with a plus +
after the
option name:
- my $verbose = ''; # option variable with default value (false)
- GetOptions ('verbose+' => \$verbose);
Using --verbose
on the command line will increment the value of
$verbose
. This way the program can keep track of how many times the
option occurred on the command line. For example, each occurrence of
--verbose
could increase the verbosity level of the program.
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
.
For options that take values it must be specified whether the option value is required or not, and what kind of value the option expects.
Three kinds of values are supported: integer numbers, floating point numbers, and strings.
If the option value is required, Getopt::Long will take the command line argument that follows the option and assign this to the option variable. If, however, the option value is specified as optional, this will only be done if that value does not look like a valid command line option itself.
- my $tag = ''; # option variable with default value
- GetOptions ('tag=s' => \$tag);
In the option specification, the option name is followed by an equals
sign =
and the letter s. The equals sign indicates that this
option requires a value. The letter s indicates that this value is
an arbitrary string. Other possible value types are i
for integer
values, and f
for floating point values. Using a colon :
instead
of the equals sign indicates that the option value is optional. In
this case, if no suitable value is supplied, string valued options get
an empty string ''
assigned, while numeric options are set to 0
.
Options sometimes take several values. For example, a program could use multiple directories to search for library files:
- --library lib/stdlib --library lib/extlib
To accomplish this behaviour, simply specify an array reference as the destination for the option:
- GetOptions ("library=s" => \@libfiles);
Alternatively, you can specify that the option can have multiple values by adding a "@", and pass a scalar reference as the destination:
- GetOptions ("library=s@" => \$libfiles);
Used with the example above, @libfiles
(or @$libfiles
) would
contain two strings upon completion: "lib/stdlib"
and
"lib/extlib"
, in that order. It is also possible to specify that
only integer or floating point numbers are acceptable values.
Often it is useful to allow comma-separated lists of values as well as multiple occurrences of the options. This is easy using Perl's split() and join() operators:
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.
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.
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:
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 --
.
In version 2.37 the first argument to the callback function was changed from string to object. This was done to make room for extensions and more detailed control. The object stringifies to the option name so this change should not introduce compatibility problems.
Here is an example of how to access the option name and value from within a subroutine:
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.
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.
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 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.
The option requires an argument of the given type. Supported types are:
String. An arbitrary sequence of characters. It is valid for the
argument to start with -
or --
.
Integer. An optional leading plus or minus sign, followed by a sequence of digits.
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').
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.
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.
Like :i
, but if the value is omitted, the number will be assigned.
Like :i
, but if the value is omitted, the current value for the
option will be incremented.
Getopt::Long can be used in an object oriented way as well:
Configuration options can be passed to the constructor:
- $p = new Getopt::Long::Parser
- config => [...configuration options...];
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.
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.
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, ... );
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.
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:
This example is fully equivalent with:
- my $len = 0;
- GetOptions ('length=i' => \$len); # will store in $len
Any mixture is possible. For example, the most frequently used options could be stored in variables while all other options get stored in the hash:
- my $verbose = 0; # frequently referred
- my $debug = 0; # frequently referred
- my %h = ('verbose' => \$verbose, 'debug' => \$debug);
- GetOptions (\%h, 'verbose', 'debug', 'filter', 'size=i');
- if ( $verbose ) { ... }
- if ( exists $h{filter} ) { ... option 'filter' was specified ... }
With bundling it is possible to set several single-character options
at once. For example if a
, v
and x
are all valid options,
- -vax
would set all three.
Getopt::Long supports two levels of bundling. To enable bundling, 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.
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
.
A special option 'name' <>
can be used to designate a subroutine
to handle non-option arguments. When GetOptions() encounters an
argument that does not look like an option, it will immediately call this
subroutine and passes it one parameter: the argument name. Well, actually
it is an object that stringifies to the argument name.
For example:
- my $width = 80;
- sub process { ... }
- GetOptions ('width=i' => \$width, '<>' => \&process);
When applied to the following command line:
- arg1 --width=72 arg2 --width=60 arg3
This will call
process("arg1")
while $width
is 80
,
process("arg2")
while $width
is 72
, and
process("arg3")
while $width
is 60
.
This feature requires configuration option permute, see section Configuring 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:
This option causes all configuration options to be reset to their default values.
This option causes all configuration options to be reset to their default values as if the environment variable POSIXLY_CORRECT had been set.
Allow option names to be abbreviated to uniqueness.
Default is enabled unless environment variable
POSIXLY_CORRECT has been set, in which case auto_abbrev
is disabled.
Allow +
to start options.
Default is enabled unless environment variable
POSIXLY_CORRECT has been set, in which case getopt_compat
is disabled.
gnu_compat
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.
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().
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
.
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.
Enabling this option will allow single-character options to be
bundled. To distinguish bundles from long option names, long options
must be introduced with --
and bundles with -
.
Note that, if you have options a
, l
and all
, and
auto_abbrev enabled, possible arguments and option settings are:
- using argument sets option(s)
- ------------------------------------------
- -a, --a a
- -l, --l l
- -al, -la, -ala, -all,... a, l
- --al, --all all
The surprising part is that --a
sets option a
(due to auto
completion), not all
.
Note: disabling bundling
also disables bundling_override
.
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.
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
.
When bundling is in effect, case is ignored on single-character options also.
Note: disabling ignore_case_always
also disables ignore_case
.
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.
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.
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 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.
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
.
The string that starts options. If a constant string is not
sufficient, see 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 --|-.
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.
Enable debugging output.
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() });
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() });
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'.
When no destination is specified for an option, GetOptions will store
the resultant value in a global variable named opt_
XXX, where
XXX is the primary name of this option. When a program executes
under use strict
(recommended), these variables must be
pre-declared with our() or use vars
.
- our $opt_length = 0;
- GetOptions ('length=i'); # will store in $opt_length
To yield a usable Perl variable, characters that are not part of the
syntax for variables are translated to underscores. For example,
--fpp-struct-return
will set the variable
$opt_fpp_struct_return
. Note that this variable resides in the
namespace of the calling program, not necessarily main
. For
example:
- GetOptions ("size=i", "sizes=i@");
with command line "-size 10 -sizes 24 -sizes 48" will perform the equivalent of the assignments
- $opt_size = 10;
- @opt_sizes = (24, 48);
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.
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.
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:
That's why they're called 'options'.
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:
to verify how your CLI passes the arguments to the program.
Are you running Windows, and did you write
- use GetOpt::Long;
(note the capital 'O')?
You can only obtain this using an alias, and Getopt::Long of at least version 2.13.
- use Getopt::Long;
- GetOptions ("help|?"); # -help and -? will both set $opt_help
Other characters that can't appear in Perl identifiers are also supported as aliases with Getopt::Long of at least version 2.39.
As of version 2.32 Getopt::Long provides auto-help, a quick and easy way to add the options --help and -? to your program, and handle them.
See auto_help
in section Configuring Getopt::Long.
Johan Vromans <jvromans@squirrel.nl>
This program is Copyright 1990,2013 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.