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Manual Reference Pages  -  POD::CONSTANTS (3)

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Pod::Constants - Include constants from POD



 use vars qw($myvar $VERSION @myarray $html %myhash);

 use Pod::Constants -trim => 1,
     Pod Section Name => \$myvar,
     Version => sub { eval },
     Some list => \@myarray,
     html => \$html,
     Some hash => \%myhash;

 =head2 Pod Section Name

 This string will be loaded into $myvar

 =head2 Version

 # This is an example of using a closure.  $_ is set to the
 # contents of the paragraph.  In this example, "eval" is
 # used to execute this code at run time.
 $VERSION = 0.17;

 =head2 Some list

 Each line from this section of the file
 will be placed into a seperate array element.
 For example, this is $myarray[2].

 =head2 Some hash

 This text will not go into the hash, because
 it doesnt look like a definition list.
     key1 => Some value (this will go into the hash)
     var2 => Some Other value (so will this)
     wtf = This wont make it in.

 =head2 %myhashs value after the above:

    ( key1 => "Some value (this will go into the hash)",
      var2 => "Some Other value (so will this)"          )

 =begin html <p>This text will be in $html</p>



This module allows you to specify those constants that should be documented in your POD, and pull them out a run time in a fairly arbitrary fashion.

Pod::Constants uses Pod::Parser to do the parsing of the source file. It has to open the source file it is called from, and does so directly either by lookup in %INC or by assuming it is $0 if the caller is main (or it can’t find %INC{caller()})


I have made this code only allow the Pod Section Name to match ‘headN’, ‘item’, ‘for’ and ‘begin’ POD sections. If you have a good reason why you think it should match other POD sections, drop me a line and if I’m convinced I’ll put it in the standard version.

For ‘for’ and ‘begin’ sections, only the first word is counted as being a part of the specifier, as opposed to ‘headN’ and ‘item’, where the entire rest of the line counts.



This function is called when we are use’d. It determines the source file by inspecting the value of caller() or $0.

The form of @args is HOOK => $where.

$where may be a scalar reference, in which case the contents of the POD section called HOOK will be loaded into $where.

$where may be an array reference, in which case the contents of the array will be the contents of the POD section called HOOK, split into lines.

$where may be a hash reference, in which case any lines with a => symbol present will have everything on the left have side of the => operator as keys and everything on the right as values. You do not need to quote either, nor have trailing commas at the end of the lines.

$where may be a code reference (sub { }), in which case the sub is called when the hook is encountered. $_ is set to the value of the POD paragraph.

You may also specify the behaviour of whitespace trimming; by default, no trimming is done except on the HOOK names. Setting -trim => 1 turns on a package global (until the next time import is called) that will trim the $_ sent for processing by the hook processing function (be it a given function, or the built-in array/hash splitters) for leading and trailing whitespace.

The name of HOOK is matched against any =head1, =head2, =item, =for, =begin value. If you specify the special hooknames *item, *head1, etc, then you will get a function that is run for every

Note that the supplied functions for array and hash splitting are exactly equivalent to fairly simple Perl blocks:


  HOOK => sub { @array = split /\n/, $_ }


  HOOK => sub {
  %hash =
      (map { map { s/^\s+|\s+$//g; $_ } split /=>/, $_ }
            (grep m/^
                    ( (?:[^=]|=[^>])+ )   # scan up to "=>"
                    ( (?:[^=]|=[^>])+ =? )# dont allow more "=>"s
                    $/x, split /\n/, $_));

Well, they’re simple if you can grok map, a regular expression like that and a functional programming style. If you can’t I’m sure it is probably voodoo to you.

Here’s the procedural equivalent:

  HOOK => sub {
     for my $line (split /\n/, $_) {
         my ($key, $value, $junk) = split /=>/, $line;
         next if $junk;
         $key =~ s/^\s+|\s+$//g
         $value =~ s/^\s+|\s+$//g
         $hash{$key} = $value;

import_from_file($filename, CW@args)

Very similar to straight import, but you specify the source filename explicitly.

    add_hook(NAME => value)

This function adds another hook, it is useful for dynamic updating of parsing through the document.

For an example, please see t/01-constants.t in the source distribution. More detailed examples will be added in a later release.


Deletes the named hooks. Companion function to add_hook


If the given value is a ref CODE, then that function is called, with $_ set to the value of the paragraph. This can be very useful for applying your own custom mutations to the POD to change it from human readable text into something your program can use.

After I added this function, I just kept on thinking of cool uses for it. The nice, succinct code you can make with it is one of Pod::Constant’s strongest features.

Below are some examples.


    Module Makefile.PL maintenance

Tired of keeping those module Makefile.PL’s up to date? Note: This method seems to break dh-make-perl.

    Example Makefile.PL

 eval "use Pod::Constants";
 ($Pod::Constants::VERSION >= 0.11)
     or die <<EOF
 ####  ERROR: This module requires Pod::Constants 0.11 or
 ####  higher to be installed.

      MODULE RELEASE => sub { ($VERSION) = m/(\d+\.\d+)/ },
      DEPENDANCIES => ($PREREQ_PM = { }),
       -trim => 1,
      NAME => sub { $ABSTRACT=$_; ($NAME) = m/(\S+)/ },
      AUTHOR => \$AUTHOR,

      NAME            => $NAME,
      PREREQ_PM        => $PREREQ_PM,
      VERSION          => $VERSION,
      ($] >= 5.005 ?    ## Add these new keywords supported since 5.005
       (ABSTRACT         => $ABSTRACT,
        AUTHOR           => $AUTHOR) : ()),

    Corresponding Module

 =head1 NAME

 MyTestModule - Demonstrate Pod::Constants Makefile.PL usefulness


 This is release 1.05 of this module.


 The following modules are required to make this module:

    Some::Module => 0.02

 =head2 AUTHOR

 Ima Twat <>


 use vars qw($VERSION);
 use Pod::Constants -trim => 1,
     MODULE RELEASE => sub { ($VERSION) = m/(\d+\.\d+) or die };


Sam Vilain, <>


I keep thinking it would be nice to be able to import an =item list into an array or something, eg for a program argument list. But I’m not too sure how it would be all that useful in practice; you’d end up putting the function names for callbacks in the pod or something (perhaps not all that bad).

Would this be useful?

 Pod::Constants::import(Foo::SECTION => \$myvar);

Debug output is not very readable


If you have any suggestions for enhancements, they are much more likely to happen if you submit them as a patch to the distribution.

Source is kept at


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perl v5.20.3 CONSTANTS (3) 2015-03-10

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