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.\" ========================================================================
.\"
.IX Title "Getargs::Long 3pm"
.TH Getargs::Long 3pm "2023-08-17" "perl v5.36.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Getargs::Long \- Named subroutine arguments, with optional type checking
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& use Getargs::Long;                     # case sensitive
\& use Getargs::Long qw(ignorecase);      # case insensitive
\&
\& # Simple, args mandatory
\& my ($val, $other) = getargs(@_, qw(val other));
\&
\& # Simple, args optional (in [] means optional)
\& my ($val, $other) = getargs(@_, [qw(val other)]);
\&
\& # Simple with typechecking, args mandatory
\& my ($val, $other) = getargs(@_, qw(val=Class::X other=ARRAY));
\&
\& # Simple with typechecking, args optional
\& my ($val, $other) = getargs(@_, [qw(val=Class::X other=ARRAY)]);
\&
\& # Faster version, building dedicated argument parsing routine
\& my ($val, $other) = cgetargs(@_, qw(val other));
\&
\& # Other cases, use full specs:
\& my ($x, $y, $z, $a, $b, $c) = xgetargs(@_,
\&
\&    # Non\-mandatory, defaults to undef unless specified otherwise
\&    \*(Aqx\*(Aq     => [\*(Aqi\*(Aq],                   # integer, no default
\&    \*(Aqy\*(Aq     => [\*(AqARRAY\*(Aq, [\*(Aqa\*(Aq, \*(Aqb\*(Aq]],   # Has a default
\&    \*(Aqz\*(Aq     => [],                      # No typecheck, can be anything
\&
\&    # Mandatory arguments
\&    \*(Aqa\*(Aq     => \*(Aqi\*(Aq,                     # integer (scalar)
\&    \*(Aqb\*(Aq     => \*(AqTYPE\*(Aq,                  # TYPE or any heir of TYPE
\&    \*(Aqc\*(Aq     => undef,                   # unspecified type but mandatory
\& );
\&
\& # Extract remaining unparsed args in @extra
\& my ($val, $other, @extra) = getargs(@_, { \-strict => 0 }, qw(val other));
\&
\& # Alter behaviour of the getargs() routines via switches in hashref
\& my ($val, $other) = getargs(@_,
\&    {
\&        \-strict         => 1,       # unknown switches are fatal
\&        \-ignorecase     => 1,       # override package\*(Aqs global
\&        \-inplace        => 1,       # edit @_ inplace: remove parsed args
\&        \-extra          => 0,       # suppress return of extra arguments
\&    },
\&    qw(val other)
\& );
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \f(CW\*(C`Getargs::Long\*(C'\fR module allows usage of named parameters in function
calls, along with optional argument type-checking.  It provides an easy
way to get at the parameters within the routine, and yields concise
descriptions for the common cases of all-mandatory and all-optional
parameter lists.
.PP
The validation of arguments can be done by a structure-driven routine
\&\fBgetargs()\fR which is fine for infrequently called routines (but should be slower),
or via a dedicated routine created and compiled on the fly the fist time it is
needed, by using the \fBcgetargs()\fR family (expected to be faster).
.PP
The \f(CW\*(C`Log::Agent\*(C'\fR module is used to report errors, which leaves to the
application the choice of the final logging method: to a file, to
\&\s-1STDERR,\s0 or to syslog.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Before going through the interface specification, a little example will
help illustrate both caller and callee sides.  Let's write a routine
that can be called as either:
.PP
.Vb 3
\& f(\-x => 1, \-y => 2, \-z => 3);  # \-switch form
\& f(x => 1, y => 2, z => 3);     # concise form (\- are optional)
\& f(y => 1, x => 2);             # order changed, z may be omitted
.Ve
.PP
Since we have an optional parameter \fIz\fR but mandatory \fIx\fR and \fIy\fR, we
can't use the short form of \fBgetargs()\fR and must therefore use \fBxgetargs()\fR:
.PP
.Vb 8
\& sub f {
\&     my ($x, $y ,$z) = xgetargs(@_,
\&         \-x => \*(Aqi\*(Aq,             # mandatory, integer
\&         \-y => \*(Aqi\*(Aq,             # mandatory, integer
\&         \-z => [\*(Aqi\*(Aq, 0],        # optional integer, defaults to 0
\&     );
\&     # code use $x, $y, $z
\& }
.Ve
.PP
That's quite simple and direct if you think of [] as \*(L"optional\*(R".  Note that
we pass \fBxgetargs()\fR a \fIreference\fR to \f(CW@_\fR.
.PP
If we had all arguments mandatory and wished to nonethless benefit from the
named specification at call time to avoid having the caller remember the
exact parameter ordering, we could write:
.PP
.Vb 4
\& sub f {
\&     my ($x, $y ,$z) = getargs(@_, qw(x=i y=i z=i));
\&     # code of f
\& }
.Ve
.PP
Without parameter type checking, that would be even more concise.  Besides,
if f() is frequently called, it might be more efficient to build a routine
dynamically to parse the arguments rather than letting \fBgetargs()\fR parse the
same data structures again and again:
.PP
.Vb 4
\& sub f {
\&     my ($x, $y ,$z) = cgetargs(@_, qw(x y z));    # \*(Aqc\*(Aq for cached/compiled
\&     # code of f
\& }
.Ve
.PP
If you call f() with an improper argument, \fBlogcroak()\fR will be called to
issue an exception from the persepective of the caller, i.e. pointing to the
place f() is called instead of within f() at the \fBgetargs()\fR call, which would
be rather useless.
.PP
Here are some more examples:
.PP
Example 1 \*(-- All mandatory:
.PP
.Vb 4
\&   sub f {
\&       my ($port, $server) = getargs(@_,
\&           qw(port=i server=HTTP::Server));
\&   }
\&
\&   f(\-server => $server, port => 80);  # or \-port, since \- is optional
\&   f(port => 80, server => $server);
\&   f(server => $server);               # WRONG: missing mandatory \-port
\&   f(server => 80, port => 80);        # WRONG: \-server not an HTTP::Server
\&   f(server => undef, port => 80);     # WRONG: \-server cannot be undef
.Ve
.PP
Example 2 \*(-- All optional
.PP
.Vb 3
\&   sub cmd {
\&       my ($a, $o) = getargs(@_, [qw(a o=s)]);
\&   }
\&
\&   cmd();                      # OK
\&   cmd(\-a => undef);           # OK \-a accepts anything, even undef
\&   cmd(\-a => 1, \-o => "..");   # OK
\&   cmd(\-a => 1, \-o => undef);  # WRONG: \-o does not accept undef
\&   cmd(\-x => 1);               # WRONG: \-x is not a known argument name
.Ve
.PP
Example 3  \*(-- Mixed optional / mandatory
.PP
.Vb 6
\&   sub f {
\&       my ($x, $z) = xgetargs(@_,
\&           \-x  => \*(Aqi\*(Aq,                 # \-x mandatory integer
\&           \-z  => [\*(Aqn\*(Aq, \-20.4],        # \-z optional, defaults to \-20.4
\&       );
\&   }
\&
\&   f(x => 1, z => {});     # WRONG: z is not a numerical value
\&   f(z => 1, x => \-2);     # OK
\&   f(\-z => 1);             # WRONG: mandatory x is missing
\&   f(\-z => undef);         # WRONG: z cannot be undef
.Ve
.PP
Example 4 \*(-- Parsing options
.PP
.Vb 7
\&   sub f {
\&       my ($x, $z) = xgetargs(@_,
\&           { \-strict => 0, \-ignorecase => 1 },
\&           \-x  => \*(Aqi\*(Aq,                 # \-x mandatory integer
\&           \-z  => [\*(Aqn\*(Aq, \-20.4],        # \-z optional, defaults to \-20.4
\&       );
\&   }
\&
\&   f(x => 1, foo => {});   # OK, \-foo ignored since not strict
\&   f(\-X => 1);             # OK, \-X actually specifies \-x with ignorecase
.Ve
.SH "INTERFACE"
.IX Header "INTERFACE"
All the routines take a mandatory first argument, called \fIarglist\fR,
which is the array containing the named arguments for the routine
(i.e. a succession of \fIname\fR => \fIvalue\fR tuples).  This array is implicitely
passed as reference, and will usually be given as \f(CW@_\fR.
.PP
All the routines take an optional \fIoptions\fR argument which comes in the
second place.  It is an hash reference containing named options that
alter the behaviour of the routine.  More details given in the Options
section.
.PP
All the routines return a list of the arguments in the order they are
specified, each \fIslot\fR in the list being either the argument value, if
present, or \f(CW\*(C`undef\*(C'\fR if missing (and not mandatory).
.SS "Simple Cases"
.IX Subsection "Simple Cases"
Simple cases are handled by \fBgetargs()\fR: named arguments should either be
\&\fIall mandatory\fR or \fIall optional\fR, and there is no provision for specifying
a default value for optional parameters.
.PP
The \fBgetargs()\fR routine and its cousin \fBcgetargs()\fR have two different interfaces,
depending on whether the arguments are all mandatory or all optional.  We'll
only specify for \fBgetargs()\fR, but the signature of \fBcgetargs()\fR is identical.
.IP "getargs \fIarglist\fR, \fIoptions\fR, \fIarg_spec1\fR, \fIarg_spec2\fR, ..." 4
.IX Item "getargs arglist, options, arg_spec1, arg_spec2, ..."
We'll be ignoring the \fIoptions\fR argument from our discussion.  See the
Options section for details.
.Sp
All the routine formal arguments specified by \fIarg_spec1\fR, \fIarg_spec2\fR,
etc... are mandatory.  If \fIarg_spec1\fR is only a name, then it specifies
a mandatory formal argument of that name, which can be of any type, even
undef.  If the name is followed by \f(CW\*(C`=type\*(C'\fR then \f(CW\*(C`type\*(C'\fR specifies the
argument type: usually a reference type, unless 'i', 'n' or 's' is used
for integer, natural and string scalars.
.Sp
Currently, types 'i', 'n' and 's' all mean the same thing: that the
argument must be a scalar.  A future implementation will probably ensure
\&'i' and 'n' hold integers and natural numbers respectively, 's' being
the placeholder for anything else that is defined.
.Sp
For instance:
.Sp
.Vb 5
\&    foo               expects mandatory "foo" of "\-foo" argument (undef ok)
\&    foo=s             idem, and argument cannot be undef or reference
\&    foo=i             value of argument \-foo must be an integer
\&    foo=My::Package   foo is a blessed object, inheriting from My::Package
\&    foo=ARRAY         foo is an ARRAY reference
.Ve
.Sp
The rule for determing whether \f(CW\*(C`foo=X\*(C'\fR means \f(CW\*(C`foo\*(C'\fR is a reference \f(CW\*(C`X\*(C'\fR
or \f(CW\*(C`foo\*(C'\fR is an object whose class is an heir of \f(CW\*(C`X\*(C'\fR depends on the
argument value at runtime: if it is an unblessed ref, strict reference
equality is expected.  If it is a blessed ref, type conformance is based
on inheritance, as you would expect.
.Sp
Example:
.Sp
.Vb 4
\&    sub f {
\&        my ($port, $server) = getargs(@_,
\&            qw(port=i server=HTTP::Server));
\&    }
.Ve
.Sp
Some calls:
.Sp
.Vb 5
\&    f(\-server => $server, port => 80);  # or \-port, since \- is optional
\&    f(port => 80, server => $server);
\&    f(server => $server);               # WRONG: missing mandatory \-port
\&    f(server => 80, port => 80);        # WRONG: \-server not an HTTP::Server
\&    f(server => undef, port => 80);     # WRONG: \-server cannot be undef
.Ve
.Sp
By default, named argument processing is case-sensitive but there is an
option to ignore case.
.IP "getargs \fIarglist\fR, \fIoptions\fR, \fIarray_ref\fR" 4
.IX Item "getargs arglist, options, array_ref"
This form specifies that all the formal arguments specified in the
\&\fIarray_ref\fR are optional.  Think of the '[' and ']' (which you'll probably
use to supply the reference as a manifest constant) as syntactic markers
for optional things.  In the traditional Unix command line description,
something like:
.Sp
.Vb 1
\&    cmd [\-a] [\-o file]
.Ve
.Sp
typically denotes that options \f(CW\*(C`\-a\*(C'\fR and \f(CW\*(C`\-o\*(C'\fR are optional, and that \f(CW\*(C`\-o\*(C'\fR
takes one argument, a file name.  To specify the same things for routine
arguments using \fBgetargs()\fR:
.Sp
.Vb 3
\&    sub cmd {
\&        my ($a, $o) = getargs(@_, [qw(a o=s)]);
\&    }
.Ve
.Sp
Here however, the \f(CW\*(C`\-a\*(C'\fR argument can be anything: we're not specifying
switches, we're specifying \fInamed\fR arguments.  Big difference.
.Sp
Some calls:
.Sp
.Vb 5
\&    cmd();                      # OK
\&    cmd(\-a => undef);           # OK \-a accepts anything, even undef
\&    cmd(\-a => 1, \-o => "..");   # OK
\&    cmd(\-a => 1, \-o => undef);  # WRONG: \-o does not accept undef
\&    cmd(\-x => 1);               # WRONG: \-x is not a known argument name
.Ve
.Sp
It is important to note that there can only be tuples when using named
arguments, which means that the routine is called with an \fIeven\fR number
of arguments.  If you forget a \f(CW\*(C`,\*(C'\fR separator between arguments, \fBgetargs()\fR
will complain about an \fIodd\fR number of arguments (provided the resulting
code still parses as valid Perl, naturally, or you'll never get a chance
to reach the execution of \fBgetargs()\fR anyway).
.IP "cgetargs \fIsame args as getargs\fR" 4
.IX Item "cgetargs same args as getargs"
The \fBcgetargs()\fR routine behaves exactly as the \fBgetargs()\fR routine: it takes
the same arguments, returns the same list.  The only difference is that
the first time it is called, it builds a routine to process the arguments,
and then calls it.
.Sp
On subsequent calls to \fBcgetargs()\fR for the same routine, the cached argument
parsing routine is re-used to analyze the arguments.  For frequently called
routines, this might be a win, even though Perl still needs to construct the
argument list to \fBcgetargs()\fR and call it.
.IP "cxgetargs \fIsame args as getargs\fR" 4
.IX Item "cxgetargs same args as getargs"
Like \fBcgetargs()\fR, but with extended specifications allowing to specify defaults
for non-mandatory arguments. Be careful: those defaults are deep-cloned and
\&\*(L"frozen\*(R", so to speak.
.SS "Complex Cases"
.IX Subsection "Complex Cases"
The \fBxgetargs()\fR routine and its cousin \fBcxgetargs()\fR (for the caching version)
allow for a more verbose description of named parameters which allows
specifying arguments that are mandatory or optional, and also give default
values to optional arguments.
.IP "xgetargs \fIarglist\fR, \fIoptions\fR, \fIname\fR => \fItype\fR, ..." 4
.IX Item "xgetargs arglist, options, name => type, ..."
We'll be ignoring the \fIoptions\fR argument from our discussion.  See Options
for details.
.Sp
There can be as many \fIname\fR => \fItype\fR tuples as necessary to describe all
the formal arguments of the routine.  The \fIname\fR refers to the argument
name, and \fItype\fR specifies both the mandatory nature and the expected type.
You may use \fIname\fR or \fI\-name\fR to specify an argument called \fIname\fR, and
the caller will also be able to spell it as he wishes.
The \fItype\fR is encoded as follows:
.Sp
.Vb 7
\&    "i"      mandatory integer (scalar)
\&    "s"      mandatory string (scalar)
\&    "TYPE"   mandatory ref of type TYPE, or heir of type TYPE
\&    undef    unspecified type, but mandatory argument
\&    ["i"]    optional integer
\&    ["s"]    optional string
\&    ["TYPE"] optional ref of type TYPE, or heir of type TYPE
.Ve
.Sp
For optional parameter, an optional second value may be inserted in the
list to specify a default value.  For instance, the tupple:
.Sp
.Vb 1
\&    \*(Aqy\*(Aq => [\*(AqHASH\*(Aq, { a => 1, b => 2 }]
.Ve
.Sp
specifies an optional named argument \fIy\fR, which is expected to be a \s-1HASH\s0
reference, and whose default value is the hash given.
.Sp
You may specify an expression as default value instead of giving a manifest
constant, but \fB\s-1BEWARE\s0\fR: the \fBcxgetargs()\fR routine will take a snapshot of
your expression when building its analyzing routine.  It's of no consequence
when using a manifest constant, but when using an expression, it will be
evaluated \fBonce\fR and the result of that evaluation will be taken as the
manifest constant to use subsequently (and this does \fBnot\fR mean the \fBsame\fR
reference will be returned, only the same topological structure as the one
we evaluated during caching).
.Sp
Example:
.Sp
.Vb 6
\&    sub f {
\&        my ($x, $z) = cxgetargs(@_,
\&            \-x  => \*(Aqi\*(Aq,                 # \-x mandatory integer
\&            \-z  => [\*(Aqn\*(Aq, \-20.4],        # \-z optional, defaults to \-20.4
\&        );
\&    }
\&
\&    f(x => 1, z => {});     # WRONG: z is not a numerical value
\&    f(z => 1, x => \-2);     # OK
\&    f(\-z => 1);             # WRONG: mandatory x is missing
\&    f(\-z => undef);         # WRONG: z cannot be undef
.Ve
.Sp
Remember that we are dealing with named parameters for a routine call,
not with option parsing.  Therefore, we are always expecting an \fIeven\fR
number of arguments, and those arguments are tuples \fIname\fR => \fIvalue\fR.
.SS "Options"
.IX Subsection "Options"
All the \fBgetargs()\fR and \fBxgetargs()\fR routines take an optional hash reference as
second argument.  Keys in this hash define options that apply locally to
the call.  In the case of caching routines, e.g. \fBcxgetargs()\fR, the options
are only considered the first time, when the analyzing routine is built,
and are ignored on subsequent calls.  Therefore, it is wise to use manifest
constants when specifying options, or use the non-caching function family
instead if your options need to be dynamically computed (please, don't do that).
.PP
Options given there must be spelled out with the leading \f(CW\*(C`\-\*(C'\fR and are
case sensitive.  To enable an option, give a true value.  For instance:
.PP
.Vb 7
\&    sub f {
\&        my ($x, $z) = cxgetargs(@_,
\&            { \-strict => 0, \-ignorecase => 1 },
\&            \-x  => \*(Aqi\*(Aq,                 # \-x mandatory integer
\&            \-z  => [\*(Aqn\*(Aq, \-20.4],        # \-z optional, defaults to \-20.4
\&        );
\&    }
.Ve
.PP
supplies two options, turning \f(CW\*(C`\-ignorecase\*(C'\fR on and \f(CW\*(C`\-strict\*(C'\fR off.
.PP
The available options are, in alphabetical order:
.IP "\-extra" 4
.IX Item "-extra"
Whether to report extra unknown arguments at the end of the argument list.
Example:
.Sp
.Vb 2
\&    my ($x, $y, @extra) = getargs(@_,
\&        { \-extra => 1, \-strict => 0 }, qw(x y));
.Ve
.Sp
Your setting is forced to false when \f(CW\*(C`\-strict\*(C'\fR is true.  The default
value is the negation of the boolean \f(CW\*(C`\-strict\*(C'\fR setting, which means
the above can be rewritten as:
.Sp
.Vb 1
\&    my ($x, $y, @extra) = getargs(@_, { \-strict => 0 }, qw(x y));
.Ve
.Sp
which will implicitely set \-extra to be true.  This is usually what you
want when not strict, i.e. get at the other parameters.  Assuming we
were writing the above for a function f(), calling:
.Sp
.Vb 1
\&    f(\-x => 1, \-y => 2, \-other => 5);
.Ve
.Sp
would set:
.Sp
.Vb 1
\&    @extra = (\-other => 5);
.Ve
.Sp
An alternative when you are not strict is to make use of the \f(CW\*(C`\-inplace\*(C'\fR
option to edit \f(CW@_\fR inplace.
.IP "\-ignorecase" 4
.IX Item "-ignorecase"
Turn case-insensitive named parameters.  False by default.  Actually, if
not explicitely specified, the default setting depends on the way
\&\f(CW\*(C`Getargs::Long\*(C'\fR was imported within the package scope.  If you said:
.Sp
.Vb 1
\&    use Getargs::Long;
.Ve
.Sp
then the default is indeed to be case-sensitive.  However, if you said:
.Sp
.Vb 1
\&    use Getargs::Long qw(ignorecase);
.Ve
.Sp
then the default for the package scope is to be case-insensitive.  You may
still specify the \f(CW\*(C`\-ignorecase\*(C'\fR option to force case sensitivity on a
per-routine basis, although I would never do such a thing and stick to a
uniform case sensitivity on a package basis.
.IP "\-inplace" 4
.IX Item "-inplace"
Whether to edit the routine's argument list inplace, removing processed
arguments as they are found and leaving unprocessed ones.  False by default.
.Sp
Your setting is forced to false when \f(CW\*(C`\-strict\*(C'\fR is true, naturally, since
an unknown argument is an error.
.IP "\-strict" 4
.IX Item "-strict"
Whether unknown named parameters are fatal.  True by default.
When \f(CW\*(C`\-strict\*(C'\fR is true, the \f(CW\*(C`\-inplace\*(C'\fR and \f(CW\*(C`\-extra\*(C'\fR options you may
specify are ignored and forced to false.
.SH "BUGS"
.IX Header "BUGS"
Currently, types 'i', 'n' and 's' all mean the same thing, but that will
change.  Don't take the current implementation's deficiency as an excuse
for lamely specifying your scalar types.
.PP
You must be careful in this implementation to list options and variables
in the very same order.  Some day, I will probably add another routine to
take arguments the way \f(CW\*(C`Getopt::Long\*(C'\fR does to cope with this ordering
problem (but it forces to spell out variables twice \*(-- once for declaration,
and once for specifying a pointer to it).
.SH "RELATED MODULE"
.IX Header "RELATED MODULE"
See Params::Validate for another take at parameter validation.  It is
a completely independant module, developped by Dave Rolsky, which may
also interest you.  Its interface and purpose are different though.
.SH "LICENSE"
.IX Header "LICENSE"
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself. See the file \s-1LICENSE\s0 in the distribution for
details.
.SH "AUTHOR"
.IX Header "AUTHOR"
The original code (written before September 15, 2004) was written by 
Raphael Manfredi <Raphael_Manfredi@pobox.com>.
.PP
Maintenance of this module is now being done by David Coppit
<david@coppit.org>.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Log::Agent, Params::Validate