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Getopt::Long(3) User Contributed Perl Documentation Getopt::Long(3)
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".
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 $tag = ''; # option variable with default value
GetOptions ('tag=s' => \$tag);
In the option specification, the option name is followed by an equals sign "=" and the
letter "s". The equals sign indicates that this option requires a value. The letter "s"
indicates that this value is an arbitrary string. Other possible value types are "i" for
integer values, and "f" for floating point values. Using a colon ":" instead of the equals
sign indicates that the option value is optional. In this case, if no suitable value is
supplied, string valued options get an empty string '' assigned, while numeric options are
set to 0.
Options with multiple values
Options sometimes take several values. For example, a program could use multiple
directories to search for library files:
--library lib/stdlib --library lib/extlib
To accomplish this behaviour, simply specify an array reference as the destination for the
option:
GetOptions ("library=s" => \@libfiles);
Alternatively, you can specify that the option can have multiple values by adding a "@",
and pass a scalar reference as the destination:
GetOptions ("library=s@" => \$libfiles);
Used with the example above, @libfiles (or @$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:
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 $verbose, but with opposite
values.
If the subroutine needs to signal an error, it should call die() with the desired error
message as its argument. GetOptions() will catch the die(), issue the error message, and
record that an error result must be returned upon completion.
If the text of the error message starts with an exclamation mark "!" it is interpreted
specially by GetOptions(). There is currently one special command implemented:
"die("!FINISH")" will cause GetOptions() to stop processing options, as if it encountered
a double dash "--".
In version 2.37 the first argument to the callback function was changed from string to
object. This was done to make room for extensions and more detailed control. The object
stringifies to the option name so this change should not introduce compatibility problems.
Here is an example of how to access the option name and value from within a subroutine:
GetOptions ('opt=i' => \&handler);
sub handler {
my ($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.
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.
: + [ desttype ]
Like ":i", but if the value is omitted, the current value for the option will be
incremented.
Advanced Possibilities
Object oriented interface
Getopt::Long can be used in an object oriented way as well:
use Getopt::Long;
$p = Getopt::Long::Parser->new;
$p->configure(...configuration options...);
if ($p->getoptions(...options descriptions...)) ...
if ($p->getoptionsfromarray( \@array, ...options descriptions...)) ...
Configuration options can be passed to the constructor:
$p = new Getopt::Long::Parser
config => [...configuration options...];
Thread Safety
Getopt::Long is thread safe when using ithreads as of Perl 5.8. It 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.
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
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.
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.
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".
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 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" 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
--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 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)
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.
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:
o A string containing the text of a message to print before printing the standard
message.
o A numeric value corresponding to the desired exit status.
o 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() 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);
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 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".
AUTHOR
Johan Vromans <jvromans AT squirrel.nl>
COPYRIGHT AND DISCLAIMER
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.
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