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Devel::AssertOS::Extending(3) User Contributed Perl Documentation Devel::AssertOS::Extending(3)


Devel::AssertOS::Extending - how to write Devel::AssertOS::* modules that check what platform they're running on


Devel::AssertOS::* modules are used by Devel::CheckOS to figure out what OS it is running on. A set of modules are provided which should correctly detect all platforms that perl *currently* runs on, as well as detecting OS 'families' like 'Unix' and 'Windows'.

You can also use Devel::AssertOS::* modules on their own to quickly check whether you're running on the right platform.

If you try to "use" a Devel::AssertOS module on the wrong platform, it will "die" by calling Devel::CheckOS::die_unsupported(). This conveniently spits out the text that CPAN-testers look for to see if your code failed simply because they're doing something as silly as testing your Solaris-only code on HPUX.


If you want to add support for new platforms, you need to write a module called Devel::AssertOS::PlatformName which looks like:

    package Devel::AssertOS::Linux;
    use Devel::CheckOS;
    use strict;
    use warnings;
    no warnings 'redefine';
    our $VERSION = '1.0';
    sub os_is { $^O =~ /^linux$/i ? 1 : 0; }
    Devel::CheckOS::die_unsupported() unless(os_is());

And that's it. The subroutine must be called "os_is" and loading the module must die in precisely that manner if your code is running on the wrong platform. It's a good idea to check $^O case-insensitively as it's not consistent. Note that it is an error to say:

    sub os_is { 1; }

and assume "well, on the wrong platform that'll never get reached because the module can't load". Because the module *can* load, and indeed *does get loaded* - some functions in Devel::CheckOS do things like:

    eval "use Devel::AssertOS::$os";

to suppress the error.

If you want to support a 'family' of OSes, then instead of matching against $^O, instead use "Devel::CheckOS::os_is" to check that we're running on any of the OSes in your family, like this:

    package Devel::AssertOS::FreeSoftware;
    use Devel::CheckOS;
    use strict;
    use warnings;
    our $VERSION = '1.0';
    sub matches { return qw(Linux FreeBSD NetBSD OpenBSD DragonflyBSD); }
    sub os_is { Devel::CheckOS::os_is(matches()); }
    sub expn { "The operating system is free-as-in-beer" }
    Devel::CheckOS::die_unsupported() unless(os_is());

You may also add a subroutine called "expn" which should return a small snippet of explanatory text. Again, see Devel::AssertOS::Unix for an example. This is particularly useful for 'family' modules.

Note the "matches" subroutine - this is so that people can query your module and see what OSes are in your family.


Two levels of name are supported. So "Devel::AssertOS::Linux::v2_6" is legal. More than two levels are not supported. Be careful to pick names that are both legal perl package names and legal filenames on all platforms. In general, this means anything that matches "/[_a-z]\w*/i".


I would like to reserve the namespace "Devel::AssertOS::OSFeatures::*". If you want to release a module that tells the user whether a particular OS feature is available (eg, whether POSIX shell redirection can be expected to work) then please discuss it with me first.


I would like to reserve the namespace "Devel::AssertOS::HWCapabilities::*". If you want to release a module that tells the user whether a particular hardware feature is available (eg, whether you have 64 bit integers) then please discuss it with me first.


I would like to reserve the namespace "Devel::AssertOS::Alias::*" for use by OS aliases. If you want to release a module that provides an alternative name for an OS please discuss it with me first.

Alias modules are simpler than normal extensions, they just need to call Devel::CheckOS::register_alias() when loaded, with the name of the alias as its first argument and the real name of the OS as the second. See Devel::AssertOS::Alias::MacOS for an example.


I welcome feedback about my code, including constructive criticism. Bug reports should be made using <>.

If you are feeling particularly generous you can encourage me in my open source endeavours by buying me something from my wishlist:



$^O in perlvar



David Cantrell <>

Thanks to David Golden for the name and ideas about the interface, and for the cpan-testers-discuss mailing list for prompting me to write it in the first place.


Copyright 2023 David Cantrell

This documentation is free-as-in-speech. It may be used, distributed and modified under the terms of the Creative Commons Attribution-Share Alike 2.0 UK: England & Wales License, whose text you may read at <>.


This documentation is also free-as-in-mason.

2023-02-05 perl v5.38.2