Params::Check(3perl) Perl Programmers Reference Guide Params::Check(3perl)
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:
• Convert all keys to lowercase
• Check if all required arguments have been provided
• Set arguments that have not been provided to the default
• Weed out arguments that are not supported and warn about them to the
user
• Validate the arguments given by the user based on strings, regexes,
lists or even subroutines
• 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 v5.40.1 2026-08-30 Params::Check(3perl)
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