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 function 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 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, hence the name Getopt::Long. This module
also supports single-character options and bundling. In this case, the
options are restricted to alphabetic characters only, and the
characters ? and -.
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:
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 to STDERR, 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:
my @libfiles = ();
GetOptions ("library=s" => \@libfiles);
Used with the example above, @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 acceptible 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:
my @libfiles = ();
GetOptions ("library=s" => \@libfiles);
@libfiles = split(/,/,join(',',@libfiles));
Of course, it is important to choose the right separator string for each purpose.
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.
my %defines = ();
GetOptions ("define=s" => \%defines);
When used with command line options:
--define os=linux --define vendor=redhat
the hash %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 acceptible 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. For a scalar or array destination, the second argument is the value to be stored. For a hash destination, the second arguments 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 exclamantion 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 --.
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.
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.
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, i.e. prefixed
by "no". E.g. "foo!" will allow --foo (a value of 1 will be
assigned) and --nofoo (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:
- or --.
0x followed by '0' .. '9', 'a' .. 'f', case
insensitive), or a binary string (0b followed by a series of '0'
and '1').
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.
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.
:i, but if the value is omitted, the number will be assigned.
: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:
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...];
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(-exitstatus => 0, -verbose => 2) if $man;
__END__
=head1 NAME
sample - Using GetOpt::Long and Pod::Usage
=head1 SYNOPSIS
sample [options] [file ...]
Options:
-help brief help message
-man full documentation
=head1 OPTIONS
=over 8
=item B<-help>
Print a brief help message and exits.
=item B<-man>
Prints the manual page and exits.
=back
=head1 DESCRIPTION
B<This program> will read the given input file(s) and do someting
useful with the contents thereof.
=cut
See Pod::Usage for details.
Sometimes, for example when there are a lot of options, having a separate variable for each of them can be cumbersome. GetOptions() supports, as an alternative mechanism, storing options in a hash.
To obtain this, a reference to a hash must be passed as the first
argument to GetOptions(). For each option that is specified on the
command line, the option value will be stored in the hash with the
option name as key. Options that are not actually used on the command
line will not be put in the hash, on other words,
exists($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 ... }
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
abiguity. 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.
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:
auto_abbrev is disabled.
+ 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.
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 succesful 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 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 suprising 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 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.
When bundling is in effect, case is ignored on single-character options also.
Note: disabling ignore_case_always also disables ignore_case.
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.
prefix_pattern.
(--|-|\+) unless environment variable
POSIXLY_CORRECT has been set, in which case it is (--|-).
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__}.
Errors that can't happen are signalled using Carp::croak().
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 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 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.
This warning is issued when the '!' modifier is applied to a short (one-character) option and bundling is in effect. E.g.,
Getopt::Long::Configure("bundling");
GetOptions("foo|f!" => \$foo);
Note that older Getopt::Long versions did not issue a warning, because the '!' modifier was applied to the first name only. This bug was fixed in 2.22.
Solution: separate the long and short names and apply the '!' to the long names only, e.g.,
GetOptions("foo!" => \$foo, "f" => \$foo);
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:
print STDERR (join("|",@ARGV),"\n");
to verify how your CLI passes the arguments to the program.
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 2002,1990 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.