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Getopt::Long(3)
NAME
Getopt::Long - Extended processing of command line options
SYNOPSIS
use Getopt::Long;
$result = GetOptions (...option-descriptions...);
DESCRIPTION
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 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, 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 the Configuring Getopt::Long entry elsewhere in this
document 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 to STDERR,
and return a false result.
A little bit less simple options
Getopt::Long supports two useful variants of simple options: negatable
options and incremental options.
A negatable option is specified with a 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:
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.
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.
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.
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 arguments: the name of the option, and the value to be
assigned. 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 "--".
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.
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, 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.
= type [ desttype ]
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.
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.
: 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.
Advanced Possibilities
Object oriented interface
Getopt::Long can be used in an object oriented way as well:
use Getopt::Long;
$p = new Getopt::Long::Parser;
$p->configure(...configuration options...);
if ($p->getoptions(...options descriptions...)) ...
Configuration options can be passed to the constructor:
$p = new Getopt::Long::Parser
config => [...configuration options...];
For thread safety, each method call will acquire an exclusive lock to the
Getopt::Long module. So don't call these methods from a callback routine!
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(-exitstatus => 0, -verbose => 2) if $man;
__END__
=head1 NAME
sample - Using GetOpt::Long and Pod::Usage
=head1 SYNOPSIS
sample [options] [file ...]
Options:
-help brief help message
-man full documentation
=head1 OPTIONS
=over 8
=item B<-help>
Print a brief help message and exits.
=item B<-man>
Prints the manual page and exits.
=back
=head1 DESCRIPTION
B<This program> will read the given input file(s) and do someting
useful with the contents thereof.
=cut
See the Pod::Usage manpage for details.
Storing options in a hash
Sometimes, for example when there are a lot of options, having a separate
variable for each of them can be cumbersome. GetOptions() supports, as an
alternative mechanism, storing options in a hash.
To obtain this, a reference to a hash must be passed as the first argument
to GetOptions(). For each option that is specified on the command line, the
option value will be stored in the hash with the option name as key.
Options that are not actually used on the command line will not be put in
the hash, on other words, "exists($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 $h{filter} ) { ... option 'filter' was specified ... }
Bundling
With bundling it is possible to set several single-character options at
once. For example if "a", "v" and "x" are all valid options,
-vax
would set all three.
Getopt::Long supports two levels of bundling. To enable bundling, a call to
Getopt::Long::Configure is required.
The first level of bundling can be enabled with:
Getopt::Long::Configure ("bundling");
Configured this way, single-character options can be bundled but long
options must always start with a double dash "--" to avoid abiguity. For
example, when "vax", "a", "v" and "x" are all valid options,
-vax
would set "a", "v" and "x", but
--vax
would set "vax".
The second level of bundling lifts this restriction. It can be enabled
with:
Getopt::Long::Configure ("bundling_override");
Now, "-vax" would set the option "vax".
When any level of bundling is enabled, option values may be inserted in the
bundle. For example:
-h24w80
is equivalent to
-h 24 -w 80
When configured for bundling, single-character options are matched case
sensitive while long options are matched case insensitive. To have the
single-character options matched case insensitive as well, use:
Getopt::Long::Configure ("bundling", "ignorecase_always");
It goes without saying that bundling can be quite confusing.
The lonesome dash
Normally, a lone dash "-" on the command line will not be considered an
option. Option processing will terminate (unless "permute" is configured)
and the dash will be left in "@ARGV".
It is possible to get special treatment for a lone dash. This can be
achieved by adding an option specification with an empty name, for example:
GetOptions ('' => \$stdio);
A lone dash on the command line will now be a legal option, and using it
will set variable "$stdio".
Argument call-back
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 the argument as a parameter.
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 the
Configuring Getopt::Long entry elsewhere in this document.
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 call-back 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
will call the call-back routine for arg1 and arg2, and
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.
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 single-character
options (and bundles) with "-".
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 long option names.
Single character options will be treated case-sensitive.
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".
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.
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 "(--|-)".
debug (default: disabled)
Enable debugging output.
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__}".
Errors that can't happen are signalled using Carp::croak().
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 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);
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.
Trouble Shooting
Warning: Ignoring '!' modifier for short option
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);
GetOptions does not return a false result when an option is not supplied
That's why they're called 'options'.
AUTHOR
Johan Vromans <jvromans@squirrel.nl>
COPYRIGHT AND DISCLAIMER
This program is Copyright 2000,1990 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.
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