NAME¶
Getopt::Long - Extended processing of command line options
SYNOPSIS¶
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
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. 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.
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 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/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.
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 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 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.
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 = 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...];
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(-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 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, the global @ARGV is not touched at all.
The following two calls behave identically:
$ret = GetOptions( ... );
$ret = GetOptionsFromArray(\@ARGV, ... );
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.
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 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".
- 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:
- •
- A string containing the text of a message to print
before printing the standard message.
- •
- A numeric value corresponding to the desired exit
status.
- •
- A reference to a hash.
If more than one argument is given then the entire argument list is assumed to
be a hash. If a hash is supplied (either as a reference or as a list) it
should contain one or more elements with the following keys:
- "-message"
- "-msg"
- The text of a message to print immediately prior to
printing the program's usage message.
- "-exitval"
- The desired exit status to pass to the
exit() function. This should be an integer,
or else the string "NOEXIT" to indicate that control should
simply be returned without terminating the invoking process.
- "-output"
- A reference to a filehandle, or the pathname of a file to
which the usage message should be written. The default is
"\*STDERR" unless the exit value is less than 2 (in which case
the default is "\*STDOUT").
You cannot tie this routine directly to an option, e.g.:
GetOptions("version" => \&VersionMessage);
Use this instead:
GetOptions("version" => sub { VersionMessage() });
- 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 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.
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
AUTHOR¶
Johan Vromans <jvromans@squirrel.nl>
COPYRIGHT AND DISCLAIMER¶
This program is Copyright 1990,2009 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.