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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,
"file=s" => \$data,
"verbose" => \$verbose);
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. Single character
options may be any alphabetic character, a question mark, and a dash.
Long options may consist of a series of letters, digits, and dashes.
Although this is currently not enforced by Getopt::Long, multiple
consecutive dashes are not allowed, and the option name must not end
with a dash.
To use Getopt::Long from a Perl program, you must include the
following line in your Perl program:
use Getopt::Long;
This will load the core of the Getopt::Long module and prepare your
program for using it. Most of the actual Getopt::Long code is not
loaded until you really call one of its functions.
In the default configuration, options names may be 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 = '';
my $all = '';
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 = '';
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 = '';
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 $tag = '';
GetOptions ('tag=s' => \$tag);
In the option specification, the option name is followed by an equals
sign = and the letter s. The equals sign indicates that this
option requires a value. The letter s indicates that this value is
an arbitrary string. Other possible value types are i for integer
values, and f for floating point values. Using a colon : instead
of the equals sign indicates that the option value is optional. In
this case, if no suitable value is supplied, string valued options get
an empty string '' assigned, while numeric options are set to 0.
Options sometimes take several values. For example, a program could
use multiple directories to search for library files:
--library lib/stdlib --library lib/extlib
To accomplish this behaviour, simply specify an array reference as the
destination for the option:
GetOptions ("library=s" => \@libfiles);
Alternatively, you can specify that the option can have multiple
values by adding a "@", and pass a scalar reference as the
destination:
GetOptions ("library=s@" => \$libfiles);
Used with the example above, @libfiles (or @$libfiles) would
contain two strings upon completion: "lib/srdlib" and
"lib/extlib", in that order. It is also possible to specify that
only integer or floating point numbers are acceptable values.
Often it is useful to allow comma-separated lists of values as well as
multiple occurrences of the options. This is easy using Perl's split()
and join() operators:
GetOptions ("library=s" => \@libfiles);
@libfiles = split(/,/,join(',',@libfiles));
Of course, it is important to choose the right separator string for
each purpose.
Warning: What follows is an experimental feature.
Options can take multiple values at once, for example
--coordinates 52.2 16.4 --rgbcolor 255 255 149
This can be accomplished by adding a repeat specifier to the option
specification. Repeat specifiers are very similar to the {...}
repeat specifiers that can be used with regular expression patterns.
For example, the above command line would be handled as follows:
GetOptions('coordinates=f{2}' => \@coor, 'rgbcolor=i{3}' => \@color);
The destination for the option must be an array or array reference.
It is also possible to specify the minimal and maximal number of
arguments an option takes. foo=s{2,4} indicates an option that
takes at least two and at most 4 arguments. foo=s{,} indicates one
or more values; foo:s{,} 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. 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 = '';
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 --.
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.
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.
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 something
useful with the contents thereof.
=cut
See the Pod::Usage manpage 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, the global @ARGV is not touched at all.
The following two calls behave identically:
$ret = GetOptions( ... );
$ret = GetOptionsFromArray(\@ARGV, ... );
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.
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');
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@');
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');
This example is fully equivalent with:
my $len = 0;
GetOptions ('length=i' => \$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;
my $debug = 0;
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.
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:
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