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Params::Check(3)	       User Contributed Perl Documentation		 Params::Check(3)

NAME
       Params::Check - A generic input parsing/checking mechanism.

SYNOPSIS
	   use Params::Check qw[check allow last_error];

	   sub fill_personal_info {
	       my %hash = @_;
	       my $x;

	       my $tmpl = {
		   firstname   => { required   => 1, defined => 1 },
		   lastname    => { required   => 1, store => \$x },
		   gender      => { required   => 1,
				    allow      => [qr/M/i, qr/F/i],
				  },
		   married     => { allow      => [0,1] },
		   age	       => { default    => 21,
				    allow      => qr/^\d+$/,
				  },

		   phone       => { allow => [ sub { return 1 if /$valid_re/ },
					       '1-800-PERL' ]
				  },
		   id_list     => { default	   => [],
				    strict_type    => 1
				  },
		   employer    => { default => 'NSA', no_override => 1 },
	       };

	       ### check() returns a hashref of parsed args on success ###
	       my $parsed_args = check( $tmpl, \%hash, $VERBOSE )
				   or die qw[Could not parse arguments!];

	       ... other code here ...
	   }

	   my $ok = allow( $colour, [qw|blue green yellow|] );

	   my $error = Params::Check::last_error();

DESCRIPTION
       Params::Check is a generic input parsing/checking mechanism.

       It allows you to validate input via a template. The only requirement is that the arguments
       must be named.

       Params::Check can do the following things for you:

       o   Convert all keys to lowercase

       o   Check if all required arguments have been provided

       o   Set arguments that have not been provided to the default

       o   Weed out arguments that are not supported and warn about them to the user

       o   Validate the arguments given by the user based on strings, regexes, lists or even
	   subroutines

       o   Enforce type integrity if required

       Most of Params::Check's power comes from its template, which we'll discuss below:

Template
       As you can see in the synopsis, based on your template, the arguments provided will be
       validated.

       The template can take a different set of rules per key that is used.

       The following rules are available:

       default
	   This is the default value if none was provided by the user.	This is also the type
	   "strict_type" will look at when checking type integrity (see below).

       required
	   A boolean flag that indicates if this argument was a required argument. If marked as
	   required and not provided, check() will fail.

       strict_type
	   This does a "ref()" check on the argument provided. The "ref" of the argument must be
	   the same as the "ref" of the default value for this check to pass.

	   This is very useful if you insist on taking an array reference as argument for
	   example.

       defined
	   If this template key is true, enforces that if this key is provided by user input, its
	   value is "defined". This just means that the user is not allowed to pass "undef" as a
	   value for this key and is equivalent to:
	       allow => sub { defined $_[0] && OTHER TESTS }

       no_override
	   This allows you to specify "constants" in your template. ie, they keys that are not
	   allowed to be altered by the user. It pretty much allows you to keep all your
	   "configurable" data in one place; the "Params::Check" template.

       store
	   This allows you to pass a reference to a scalar, in which the data will be stored:

	       my $x;
	       my $args = check(foo => { default => 1, store => \$x }, $input);

	   This is basically shorthand for saying:

	       my $args = check( { foo => { default => 1 }, $input );
	       my $x	= $args->{foo};

	   You can alter the global variable $Params::Check::NO_DUPLICATES to control whether the
	   "store"'d key will still be present in your result set. See the "Global Variables"
	   section below.

       allow
	   A set of criteria used to validate a particular piece of data if it has to adhere to
	   particular rules.

	   See the "allow()" function for details.

Functions
   check( \%tmpl, \%args, [$verbose] );
       This function is not exported by default, so you'll have to ask for it via:

	   use Params::Check qw[check];

       or use its fully qualified name instead.

       "check" takes a list of arguments, as follows:

       Template
	   This is a hash reference which contains a template as explained in the "SYNOPSIS" and
	   "Template" section.

       Arguments
	   This is a reference to a hash of named arguments which need checking.

       Verbose
	   A boolean to indicate whether "check" should be verbose and warn about what went wrong
	   in a check or not.

	   You can enable this program wide by setting the package variable
	   $Params::Check::VERBOSE to a true value. For details, see the section on "Global
	   Variables" below.

       "check" will return when it fails, or a hashref with lowercase keys of parsed arguments
       when it succeeds.

       So a typical call to check would look like this:

	   my $parsed = check( \%template, \%arguments, $VERBOSE )
			   or warn q[Arguments could not be parsed!];

       A lot of the behaviour of "check()" can be altered by setting package variables. See the
       section on "Global Variables" for details on this.

   allow( $test_me, \@criteria );
       The function that handles the "allow" key in the template is also available for
       independent use.

       The function takes as first argument a key to test against, and as second argument any
       form of criteria that are also allowed by the "allow" key in the template.

       You can use the following types of values for allow:

       string
	   The provided argument MUST be equal to the string for the validation to pass.

       regexp
	   The provided argument MUST match the regular expression for the validation to pass.

       subroutine
	   The provided subroutine MUST return true in order for the validation to pass and the
	   argument accepted.

	   (This is particularly useful for more complicated data).

       array ref
	   The provided argument MUST equal one of the elements of the array ref for the
	   validation to pass. An array ref can hold all the above values.

       It returns true if the key matched the criteria, or false otherwise.

   last_error()
       Returns a string containing all warnings and errors reported during the last time "check"
       was called.

       This is useful if you want to report then some other way than "carp"'ing when the verbose
       flag is on.

       It is exported upon request.

Global Variables
       The behaviour of Params::Check can be altered by changing the following global variables:

   $Params::Check::VERBOSE
       This controls whether Params::Check will issue warnings and explanations as to why certain
       things may have failed.	If you set it to 0, Params::Check will not output any warnings.

       The default is 1 when warnings are enabled, 0 otherwise;

   $Params::Check::STRICT_TYPE
       This works like the "strict_type" option you can pass to "check", which will turn on
       "strict_type" globally for all calls to "check".

       The default is 0;

   $Params::Check::ALLOW_UNKNOWN
       If you set this flag, unknown options will still be present in the return value, rather
       than filtered out. This is useful if your subroutine is only interested in a few
       arguments, and wants to pass the rest on blindly to perhaps another subroutine.

       The default is 0;

   $Params::Check::STRIP_LEADING_DASHES
       If you set this flag, all keys passed in the following manner:

	   function( -key => 'val' );

       will have their leading dashes stripped.

   $Params::Check::NO_DUPLICATES
       If set to true, all keys in the template that are marked as to be stored in a scalar, will
       also be removed from the result set.

       Default is false, meaning that when you use "store" as a template key, "check" will put it
       both in the scalar you supplied, as well as in the hashref it returns.

   $Params::Check::PRESERVE_CASE
       If set to true, Params::Check will no longer convert all keys from the user input to
       lowercase, but instead expect them to be in the case the template provided. This is useful
       when you want to use similar keys with different casing in your templates.

       Understand that this removes the case-insensitivity feature of this module.

       Default is 0;

   $Params::Check::ONLY_ALLOW_DEFINED
       If set to true, Params::Check will require all values passed to be "defined". If you wish
       to enable this on a 'per key' basis, use the template option "defined" instead.

       Default is 0;

   $Params::Check::SANITY_CHECK_TEMPLATE
       If set to true, Params::Check will sanity check templates, validating for errors and
       unknown keys. Although very useful for debugging, this can be somewhat slow in hot-code
       and large loops.

       To disable this check, set this variable to "false".

       Default is 1;

   $Params::Check::WARNINGS_FATAL
       If set to true, Params::Check will "croak" when an error during template validation
       occurs, rather than return "false".

       Default is 0;

   $Params::Check::CALLER_DEPTH
       This global modifies the argument given to "caller()" by "Params::Check::check()" and is
       useful if you have a custom wrapper function around "Params::Check::check()". The value
       must be an integer, indicating the number of wrapper functions inserted between the real
       function call and "Params::Check::check()".

       Example wrapper function, using a custom stacktrace:

	   sub check {
	       my ($template, $args_in) = @_;

	       local $Params::Check::WARNINGS_FATAL = 1;
	       local $Params::Check::CALLER_DEPTH = $Params::Check::CALLER_DEPTH + 1;
	       my $args_out = Params::Check::check($template, $args_in);

	       my_stacktrace(Params::Check::last_error) unless $args_out;

	       return $args_out;
	   }

       Default is 0;

Acknowledgements
       Thanks to Richard Soderberg for his performance improvements.

BUG REPORTS
       Please report bugs or other issues to <bug-params-check@rt.cpan.org>.

AUTHOR
       This module by Jos Boumans <kane@cpan.org>.

COPYRIGHT
       This library is free software; you may redistribute and/or modify it under the same terms
       as Perl itself.

perl v5.16.3				    2013-06-20				 Params::Check(3)
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