{
    "mode": "man",
    "parameter": "perlmodstyle",
    "section": "1",
    "url": "https://www.chedong.com/phpMan.php/man/perlmodstyle/1/json",
    "generated": "2026-06-10T16:22:45Z",
    "sections": {
        "NAME": {
            "content": "perlmodstyle - Perl module style guide\n",
            "subsections": []
        },
        "INTRODUCTION": {
            "content": "This document attempts to describe the Perl Community's \"best practice\" for writing Perl\nmodules.  It extends the recommendations found in perlstyle , which should be considered\nrequired reading before reading this document.\n\nWhile this document is intended to be useful to all module authors, it is particularly aimed\nat authors who wish to publish their modules on CPAN.\n\nThe focus is on elements of style which are visible to the users of a module, rather than\nthose parts which are only seen by the module's developers.  However, many of the guidelines\npresented in this document can be extrapolated and applied successfully to a module's\ninternals.\n\nThis document differs from perlnewmod in that it is a style guide rather than a tutorial on\ncreating CPAN modules.  It provides a checklist against which modules can be compared to\ndetermine whether they conform to best practice, without necessarily describing in detail how\nto achieve this.\n\nAll the advice contained in this document has been gleaned from extensive conversations with\nexperienced CPAN authors and users.  Every piece of advice given here is the result of\nprevious mistakes.  This information is here to help you avoid the same mistakes and the\nextra work that would inevitably be required to fix them.\n\nThe first section of this document provides an itemized checklist; subsequent sections\nprovide a more detailed discussion of the items on the list.  The final section, \"Common\nPitfalls\", describes some of the most popular mistakes made by CPAN authors.\n",
            "subsections": []
        },
        "QUICK CHECKLIST": {
            "content": "For more detail on each item in this checklist, see below.\n",
            "subsections": [
                {
                    "name": "Before you start",
                    "content": "•   Don't re-invent the wheel\n\n•   Patch, extend or subclass an existing module where possible\n\n•   Do one thing and do it well\n\n•   Choose an appropriate name\n\n•   Get feedback before publishing\n"
                },
                {
                    "name": "The API",
                    "content": "•   API should be understandable by the average programmer\n\n•   Simple methods for simple tasks\n\n•   Separate functionality from output\n\n•   Consistent naming of subroutines or methods\n\n•   Use named parameters (a hash or hashref) when there are more than two parameters\n"
                },
                {
                    "name": "Stability",
                    "content": "•   Ensure your module works under \"use strict\" and \"-w\"\n\n•   Stable modules should maintain backwards compatibility\n"
                },
                {
                    "name": "Documentation",
                    "content": "•   Write documentation in POD\n\n•   Document purpose, scope and target applications\n\n•   Document each publicly accessible method or subroutine, including params and return\nvalues\n\n•   Give examples of use in your documentation\n\n•   Provide a README file and perhaps also release notes, changelog, etc\n\n•   Provide links to further information (URL, email)\n"
                },
                {
                    "name": "Release considerations",
                    "content": "•   Specify pre-requisites in Makefile.PL or Build.PL\n\n•   Specify Perl version requirements with \"use\"\n\n•   Include tests with your module\n\n•   Choose a sensible and consistent version numbering scheme (X.YY is the common Perl module\nnumbering scheme)\n\n•   Increment the version number for every change, no matter how small\n\n•   Package the module using \"make dist\"\n\n•   Choose an appropriate license (GPL/Artistic is a good default)\n"
                }
            ]
        },
        "BEFORE YOU START WRITING A MODULE": {
            "content": "Try not to launch headlong into developing your module without spending some time thinking\nfirst.  A little forethought may save you a vast amount of effort later on.\n",
            "subsections": [
                {
                    "name": "Has it been done before?",
                    "content": "You may not even need to write the module.  Check whether it's already been done in Perl, and\navoid re-inventing the wheel unless you have a good reason.\n\nGood places to look for pre-existing modules include MetaCPAN <https://metacpan.org> and\nPrePAN <http://prepan.org> and asking on \"module-authors@perl.org\"\n(<https://lists.perl.org/list/module-authors.html>).\n\nIf an existing module almost does what you want, consider writing a patch, writing a\nsubclass, or otherwise extending the existing module rather than rewriting it.\n"
                },
                {
                    "name": "Do one thing and do it well",
                    "content": "At the risk of stating the obvious, modules are intended to be modular.  A Perl developer\nshould be able to use modules to put together the building blocks of their application.\nHowever, it's important that the blocks are the right shape, and that the developer shouldn't\nhave to use a big block when all they need is a small one.\n\nYour module should have a clearly defined scope which is no longer than a single sentence.\nCan your module be broken down into a family of related modules?\n\nBad example:\n\n\"FooBar.pm provides an implementation of the FOO protocol and the related BAR standard.\"\n\nGood example:\n\n\"Foo.pm provides an implementation of the FOO protocol.  Bar.pm implements the related BAR\nprotocol.\"\n\nThis means that if a developer only needs a module for the BAR standard, they should not be\nforced to install libraries for FOO as well.\n"
                },
                {
                    "name": "What's in a name?",
                    "content": "Make sure you choose an appropriate name for your module early on.  This will help people\nfind and remember your module, and make programming with your module more intuitive.\n\nWhen naming your module, consider the following:\n\n•   Be descriptive (i.e. accurately describes the purpose of the module).\n\n•   Be consistent with existing modules.\n\n•   Reflect the functionality of the module, not the implementation.\n\n•   Avoid starting a new top-level hierarchy, especially if a suitable hierarchy already\nexists under which you could place your module.\n"
                },
                {
                    "name": "Get feedback before publishing",
                    "content": "If you have never uploaded a module to CPAN before (and even if you have), you are strongly\nencouraged to get feedback on PrePAN <http://prepan.org>.  PrePAN is a site dedicated to\ndiscussing ideas for CPAN modules with other Perl developers and is a great resource for new\n(and experienced) Perl developers.\n\nYou should also try to get feedback from people who are already familiar with the module's\napplication domain and the CPAN naming system.  Authors of similar modules, or modules with\nsimilar names, may be a good place to start, as are community sites like Perl Monks\n<https://www.perlmonks.org>.\n"
                }
            ]
        },
        "DESIGNING AND WRITING YOUR MODULE": {
            "content": "Considerations for module design and coding:\n",
            "subsections": [
                {
                    "name": "To OO or not to OO?",
                    "content": "Your module may be object oriented (OO) or not, or it may have both kinds of interfaces\navailable.  There are pros and cons of each technique, which should be considered when you\ndesign your API.\n\nIn Perl Best Practices (copyright 2004, Published by O'Reilly Media, Inc.), Damian Conway\nprovides a list of criteria to use when deciding if OO is the right fit for your problem:\n\n•   The system being designed is large, or is likely to become large.\n\n•   The data can be aggregated into obvious structures, especially if there's a large amount\nof data in each aggregate.\n\n•   The various types of data aggregate form a natural hierarchy that facilitates the use of\ninheritance and polymorphism.\n\n•   You have a piece of data on which many different operations are applied.\n\n•   You need to perform the same general operations on related types of data, but with slight\nvariations depending on the specific type of data the operations are applied to.\n\n•   It's likely you'll have to add new data types later.\n\n•   The typical interactions between pieces of data are best represented by operators.\n\n•   The implementation of individual components of the system is likely to change over time.\n\n•   The system design is already object-oriented.\n\n•   Large numbers of other programmers will be using your code modules.\n\nThink carefully about whether OO is appropriate for your module.  Gratuitous object\norientation results in complex APIs which are difficult for the average module user to\nunderstand or use.\n"
                },
                {
                    "name": "Designing your API",
                    "content": "Your interfaces should be understandable by an average Perl programmer.  The following\nguidelines may help you judge whether your API is sufficiently straightforward:\n\nWrite simple routines to do simple things.\nIt's better to have numerous simple routines than a few monolithic ones.  If your routine\nchanges its behaviour significantly based on its arguments, it's a sign that you should\nhave two (or more) separate routines.\n\nSeparate functionality from output.\nReturn your results in the most generic form possible and allow the user to choose how to\nuse them.  The most generic form possible is usually a Perl data structure which can then\nbe used to generate a text report, HTML, XML, a database query, or whatever else your\nusers require.\n\nIf your routine iterates through some kind of list (such as a list of files, or records\nin a database) you may consider providing a callback so that users can manipulate each\nelement of the list in turn.  File::Find provides an example of this with its\n\"find(\\&wanted, $dir)\" syntax.\n\nProvide sensible shortcuts and defaults.\nDon't require every module user to jump through the same hoops to achieve a simple\nresult.  You can always include optional parameters or routines for more complex or non-\nstandard behaviour.  If most of your users have to type a few almost identical lines of\ncode when they start using your module, it's a sign that you should have made that\nbehaviour a default.  Another good indicator that you should use defaults is if most of\nyour users call your routines with the same arguments.\n\nNaming conventions\nYour naming should be consistent.  For instance, it's better to have:\n\ndisplayday();\ndisplayweek();\ndisplayyear();\n\nthan\n\ndisplayday();\nweekdisplay();\nshowyear();\n\nThis applies equally to method names, parameter names, and anything else which is visible\nto the user (and most things that aren't!)\n\nParameter passing\nUse named parameters.  It's easier to use a hash like this:\n\n$obj->dosomething(\nname => \"wibble\",\ntype => \"text\",\nsize => 1024,\n);\n\n... than to have a long list of unnamed parameters like this:\n\n$obj->dosomething(\"wibble\", \"text\", 1024);\n\nWhile the list of arguments might work fine for one, two or even three arguments, any\nmore arguments become hard for the module user to remember, and hard for the module\nauthor to manage.  If you want to add a new parameter you will have to add it to the end\nof the list for backward compatibility, and this will probably make your list order\nunintuitive.  Also, if many elements may be undefined you may see the following\nunattractive method calls:\n\n$obj->dosomething(undef, undef, undef, undef, undef, 1024);\n\nProvide sensible defaults for parameters which have them.  Don't make your users specify\nparameters which will almost always be the same.\n\nThe issue of whether to pass the arguments in a hash or a hashref is largely a matter of\npersonal style.\n\nThe use of hash keys starting with a hyphen (\"-name\") or entirely in upper case (\"NAME\")\nis a relic of older versions of Perl in which ordinary lower case strings were not\nhandled correctly by the \"=>\" operator.  While some modules retain uppercase or\nhyphenated argument keys for historical reasons or as a matter of personal style, most\nnew modules should use simple lower case keys.  Whatever you choose, be consistent!\n"
                },
                {
                    "name": "Strictness and warnings",
                    "content": "Your module should run successfully under the strict pragma and should run without generating\nany warnings.  Your module should also handle taint-checking where appropriate, though this\ncan cause difficulties in many cases.\n"
                },
                {
                    "name": "Backwards compatibility",
                    "content": "Modules which are \"stable\" should not break backwards compatibility without at least a long\ntransition phase and a major change in version number.\n"
                },
                {
                    "name": "Error handling and messages",
                    "content": "When your module encounters an error it should do one or more of:\n\n•   Return an undefined value.\n\n•   set $Module::errstr or similar (\"errstr\" is a common name used by DBI and other popular\nmodules; if you choose something else, be sure to document it clearly).\n\n•   \"warn()\" or \"carp()\" a message to STDERR.\n\n•   \"croak()\" only when your module absolutely cannot figure out what to do.  (\"croak()\" is a\nbetter version of \"die()\" for use within modules, which reports its errors from the\nperspective of the caller.  See Carp for details of \"croak()\", \"carp()\" and other useful\nroutines.)\n\n•   As an alternative to the above, you may prefer to throw exceptions using the Error\nmodule.\n\nConfigurable error handling can be very useful to your users.  Consider offering a choice of\nlevels for warning and debug messages, an option to send messages to a separate file, a way\nto specify an error-handling routine, or other such features.  Be sure to default all these\noptions to the commonest use.\n"
                }
            ]
        },
        "DOCUMENTING YOUR MODULE": {
            "content": "POD\nYour module should include documentation aimed at Perl developers.  You should use Perl's\n\"plain old documentation\" (POD) for your general technical documentation, though you may wish\nto write additional documentation (white papers, tutorials, etc) in some other format.  You\nneed to cover the following subjects:\n\n•   A synopsis of the common uses of the module\n\n•   The purpose, scope and target applications of your module\n\n•   Use of each publicly accessible method or subroutine, including parameters and return\nvalues\n\n•   Examples of use\n\n•   Sources of further information\n\n•   A contact email address for the author/maintainer\n\nThe level of detail in Perl module documentation generally goes from less detailed to more\ndetailed.  Your SYNOPSIS section should contain a minimal example of use (perhaps as little\nas one line of code; skip the unusual use cases or anything not needed by most users); the\nDESCRIPTION should describe your module in broad terms, generally in just a few paragraphs;\nmore detail of the module's routines or methods, lengthy code examples, or other in-depth\nmaterial should be given in subsequent sections.\n\nIdeally, someone who's slightly familiar with your module should be able to refresh their\nmemory without hitting \"page down\".  As your reader continues through the document, they\nshould receive a progressively greater amount of knowledge.\n\nThe recommended order of sections in Perl module documentation is:\n\n•   NAME\n\n•   SYNOPSIS\n\n•   DESCRIPTION\n\n•   One or more sections or subsections giving greater detail of available methods and\nroutines and any other relevant information.\n\n•   BUGS/CAVEATS/etc\n\n•   AUTHOR\n\n•   SEE ALSO\n\n•   COPYRIGHT and LICENSE\n\nKeep your documentation near the code it documents (\"inline\" documentation).  Include POD for\na given method right above that method's subroutine.  This makes it easier to keep the\ndocumentation up to date, and avoids having to document each piece of code twice (once in POD\nand once in comments).\n",
            "subsections": [
                {
                    "name": "README, INSTALL, release notes, changelogs",
                    "content": "Your module should also include a README file describing the module and giving pointers to\nfurther information (website, author email).\n\nAn INSTALL file should be included, and should contain simple installation instructions.\nWhen using ExtUtils::MakeMaker this will usually be:\n\nperl Makefile.PL\nmake\nmake test\nmake install\n\nWhen using Module::Build, this will usually be:\n\nperl Build.PL\nperl Build\nperl Build test\nperl Build install\n\nRelease notes or changelogs should be produced for each release of your software describing\nuser-visible changes to your module, in terms relevant to the user.\n\nUnless you have good reasons for using some other format (for example, a format used within\nyour company), the convention is to name your changelog file \"Changes\", and to follow the\nsimple format described in CPAN::Changes::Spec.\n"
                }
            ]
        },
        "RELEASE CONSIDERATIONS": {
            "content": "",
            "subsections": [
                {
                    "name": "Version numbering",
                    "content": "Version numbers should indicate at least major and minor releases, and possibly sub-minor\nreleases.  A major release is one in which most of the functionality has changed, or in which\nmajor new functionality is added.  A minor release is one in which a small amount of\nfunctionality has been added or changed.  Sub-minor version numbers are usually used for\nchanges which do not affect functionality, such as documentation patches.\n\nThe most common CPAN version numbering scheme looks like this:\n\n1.00, 1.10, 1.11, 1.20, 1.30, 1.31, 1.32\n\nA correct CPAN version number is a floating point number with at least 2 digits after the\ndecimal.  You can test whether it conforms to CPAN by using\n\nperl -MExtUtils::MakeMaker -le 'print MM->parseversion(shift)' \\\n'Foo.pm'\n\nIf you want to release a 'beta' or 'alpha' version of a module but don't want CPAN.pm to list\nit as most recent use an '' after the regular version number followed by at least 2 digits,\neg. 1.2001.  If you do this, the following idiom is recommended:\n\nour $VERSION = \"1.1201\"; # so CPAN distribution will have\n# right filename\nour $XSVERSION = $VERSION; # only needed if you have XS code\n$VERSION = eval $VERSION; # so \"use Module 0.002\" won't warn on\n# underscore\n\nWith that trick MakeMaker will only read the first line and thus read the underscore, while\nthe perl interpreter will evaluate the $VERSION and convert the string into a number.  Later\noperations that treat $VERSION as a number will then be able to do so without provoking a\nwarning about $VERSION not being a number.\n\nNever release anything (even a one-word documentation patch) without incrementing the number.\nEven a one-word documentation patch should result in a change in version at the sub-minor\nlevel.\n\nOnce picked, it is important to stick to your version scheme, without reducing the number of\ndigits.  This is because \"downstream\" packagers, such as the FreeBSD ports system, interpret\nthe version numbers in various ways.  If you change the number of digits in your version\nscheme, you can confuse these systems so they get the versions of your module out of order,\nwhich is obviously bad.\n"
                },
                {
                    "name": "Pre-requisites",
                    "content": "Module authors should carefully consider whether to rely on other modules, and which modules\nto rely on.\n\nMost importantly, choose modules which are as stable as possible.  In order of preference:\n\n•   Core Perl modules\n\n•   Stable CPAN modules\n\n•   Unstable CPAN modules\n\n•   Modules not available from CPAN\n\nSpecify version requirements for other Perl modules in the pre-requisites in your Makefile.PL\nor Build.PL.\n\nBe sure to specify Perl version requirements both in Makefile.PL or Build.PL and with\n\"require 5.6.1\" or similar.  See the section on \"use VERSION\" of \"require\" in perlfunc for\ndetails.\n"
                },
                {
                    "name": "Testing",
                    "content": "All modules should be tested before distribution (using \"make disttest\"), and the tests\nshould also be available to people installing the modules (using \"make test\").  For\nModule::Build you would use the \"make test\" equivalent \"perl Build test\".\n\nThe importance of these tests is proportional to the alleged stability of a module.  A module\nwhich purports to be stable or which hopes to achieve wide use should adhere to as strict a\ntesting regime as possible.\n\nUseful modules to help you write tests (with minimum impact on your development process or\nyour time) include Test::Simple, Carp::Assert and Test::Inline.  For more sophisticated test\nsuites there are Test::More and Test::MockObject.\n"
                },
                {
                    "name": "Packaging",
                    "content": "Modules should be packaged using one of the standard packaging tools.  Currently you have the\nchoice between ExtUtils::MakeMaker and the more platform independent Module::Build, allowing\nmodules to be installed in a consistent manner.  When using ExtUtils::MakeMaker, you can use\n\"make dist\" to create your package.  Tools exist to help you to build your module in a\nMakeMaker-friendly style.  These include ExtUtils::ModuleMaker and h2xs.  See also\nperlnewmod.\n"
                },
                {
                    "name": "Licensing",
                    "content": "Make sure that your module has a license, and that the full text of it is included in the\ndistribution (unless it's a common one and the terms of the license don't require you to\ninclude it).\n\nIf you don't know what license to use, dual licensing under the GPL and Artistic licenses\n(the same as Perl itself) is a good idea.  See perlgpl and perlartistic.\n"
                }
            ]
        },
        "COMMON PITFALLS": {
            "content": "",
            "subsections": [
                {
                    "name": "Reinventing the wheel",
                    "content": "There are certain application spaces which are already very, very well served by CPAN.  One\nexample is templating systems, another is date and time modules, and there are many more.\nWhile it is a rite of passage to write your own version of these things, please consider\ncarefully whether the Perl world really needs you to publish it.\n"
                },
                {
                    "name": "Trying to do too much",
                    "content": "Your module will be part of a developer's toolkit.  It will not, in itself, form the entire\ntoolkit.  It's tempting to add extra features until your code is a monolithic system rather\nthan a set of modular building blocks.\n"
                },
                {
                    "name": "Inappropriate documentation",
                    "content": "Don't fall into the trap of writing for the wrong audience.  Your primary audience is a\nreasonably experienced developer with at least a moderate understanding of your module's\napplication domain, who's just downloaded your module and wants to start using it as quickly\nas possible.\n\nTutorials, end-user documentation, research papers, FAQs etc are not appropriate in a\nmodule's main documentation.  If you really want to write these, include them as sub-\ndocuments such as \"My::Module::Tutorial\" or \"My::Module::FAQ\" and provide a link in the SEE\nALSO section of the main documentation.\n"
                }
            ]
        },
        "SEE ALSO": {
            "content": "perlstyle\nGeneral Perl style guide\n\nperlnewmod\nHow to create a new module\n\nperlpod\nPOD documentation\n\npodchecker\nVerifies your POD's correctness\n\nPackaging Tools\nExtUtils::MakeMaker, Module::Build\n\nTesting tools\nTest::Simple, Test::Inline, Carp::Assert, Test::More, Test::MockObject\n\n<https://pause.perl.org/>\nPerl Authors Upload Server.  Contains links to information for module authors.\n\nAny good book on software engineering\n",
            "subsections": []
        },
        "AUTHOR": {
            "content": "Kirrily \"Skud\" Robert <skud@cpan.org>\n\n\n\nperl v5.34.0                                 2025-07-25                              PERLMODSTYLE(1)",
            "subsections": []
        }
    },
    "summary": "perlmodstyle - Perl module style guide",
    "flags": [],
    "examples": [],
    "see_also": []
}