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Params::Check(3pm)     Perl Programmers Reference Guide     Params::Check(3pm)


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


           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();


       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:


       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:

           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).

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

           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.

           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 }

           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.

           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.

           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.


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

           use Params::Check qw[check];

       or use its fully qualified name instead.

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

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

           This is a reference to a hash of named arguments which need

           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:

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

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

           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

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

       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:

       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;

       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;

       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;

       If you set this flag, all keys passed in the following manner:

           function( -key => 'val' );

       will have their leading dashes stripped.

       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.

       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

       Default is 0;

       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;

       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;

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

       Default is 0;

       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;


       Thanks to Richard Soderberg for his performance improvements.


       Please report bugs or other issues to <>.


       This module by Jos Boumans <>.


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

perl v5.24.0                      2016-02-05                Params::Check(3pm)

perl 5.24 - Generated Fri Nov 18 19:23:39 CST 2016
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