I'm have Perl 5.8 installed on all of our servers and wanted to use the DBI and DBD::Oracle modules to access our databases. My main concern is with the newer versions of perl the DBI and DBD modules will stop working with 5.8. Then I'd have to upgrade every server to the newest perl version.
My question is as perl itself becomes later versions and modules are developed for them will they still be backwards compatible? "CPAN does not carry all ancient releases and patchlevels of Perl", if I create documentation saying run "cpan -i DBI" if the newest version of DBI will not function with 5.8?
There is no guarantee.
In general, you want to use the same versions of the modules on all your systems. If you use different versions then you will have different bugs and features available on different servers.
I'd suggest creating Debs / RPMS / etc for the ones you are going to use and then run a package repository that all your servers share.
Not absolutely, but in general perl is pretty gentle about breaking code, with not many breaking changes, and long deprecation cycles on the ones that do happen. A pretty hefty portion of the code that was uploaded to CPAN in 1999 will run without modification in perl 5.14.
Since perl 5.12, the perl release cycle has become shorter, and the deprecation periods have also become shorter, which is cause for concern, but at the same time the concept of feature versioning has gained currency. The idea is that code may declare the version of perl that it's targeting with use VERSION (e.g. use 5.16.0), and any code that doesn't declare a version is assumed to be targeting approximately 5.10. When code that targets an older perl version is run on a newer perl version, newer features that might cause compatibility issues (e.g. new keywords) are disabled, and old misfeatures may be re-enabled in the name of compatibility. This isn't an absolute guarantee, but it will be adhered to as much as practical.
More information about back-compatibility and deprecation is in perlpolicy.
In general, no. There are a lot of great new features in recent releases of Perl (smart match operator, the // operator, for two one example) that are not backwards compatible. Many authors will decide to take advantage of these features rather than keep their modules compatible with older versions of Perl.
Check the CPAN Tester's Matrix of a module, including the link about the max version that passes all of the distribution's tests, to get an idea of what versions of Perl are compatible with each version of a module.
cpan -i Some::Module will indeed attempt to install the latest version of the module Some::Module, but with a little research, it can be used to install older versions too. You need to find or guess the author of an older version and provide the path to the distribution on the CPAN mirror servers. For example,
cpan -i J/JF/JFRIEDL/Yahoo-Search-1.9.12.tar.gz
cpan -i A/AS/ASG/List-Gen-0.80.tar.gz
CPAN authors may delete their older distributions from CPAN. But even then, the distribution is available at the BackPAN if you're willing to download, unpack, and build the distribution yourself.
Related
For example I believe that the Encode module is considered a core module and shipped with every copy of Perl. It has its own page on Perldoc:
https://perldoc.perl.org/Encode.html
...but it is also available on CPAN:
http://search.cpan.org/~dankogai/Encode-2.92/Encode.pm
From skimming the two documents, it seems that they contain the same text. So why put it in both places? Is it just so that CPAN can be used to lookup documentation on "any Perl module"?
Such modules are said to be "dual-life" modules.
So users can upgrade the module without upgrading perl itself.
So developers can release fixes and updates to the module on a different schedule (e.g. more often) than perl itself.
Or maybe the module started on CPAN, and it was later added to the perl distro (e.g. because a module in the tool chain requires it).
Or maybe the module is in the process of being removed from the Perl distro.
Also making a core library available at CPAN allows to easily upgrade from the version shipped with Perl to get the latest improvements and bug fixes.
For example, Encode versions shipped with some versions of perl:
Perl Encode
v5.22.4 2.72_01
v5.24.2 2.80_01
v5.26.1 2.88
(retrieved with corelist -a Encode). Any of these can be readily updated to the latest Encode 2.92.
Is there a command line switch or any other easy way that I can check the compatibility of my module with different versions of perl? I understand that if I put use 5.6.1; at the top of a script, the script will have any features later than 5.6.1 disabled. But if I have a module which uses several other modules and so on, I need a quicker way to check what minimum version of Perl to require in my Makefile.PL or Build.PL.
Run your module against Perl::MinimumVersion.
use v5.6.1 and similar will primarily raise a compile-time error if the version of Perl in use is older than that specified. In addition, the corresponding feature bundle is enabled, and if the version is v5.11 or higher, the strict pragma is enabled as well.
use v5.6.1 will not make Perl v5.8 behave like v5.6.1, and there is no way of achieving this. Even in later versions it is only features that can be controlled using the feature pragma that are adjusted to a given version.
To test your module you will have to install each different version of Perl and test it separately
You can just install different versions of perl and test against those. I install them by hand in different locations but if you want to automate that, use perlbrew.
There might be scripts or strategies that try to find the minimum version of perl needed, but everything i tried several years ago to obtain and aggregate the minimum perl version i found clunky and unreliable. Which of course doesn't mean, that it doesn't exist or can't be done, but just that i couldn't find it.
What is a "dual-life" module? It's mentioned in the perldelta for Perl 5.14.
Dual life modules are modules that exist in two disconnected source repositories, commonly meaning both in the Perl core (those libraries distributed with perl), and on CPAN.
The CPAN version may be updated more frequently than the core version. The core version may have been tested on more platforms.
In the context of the link you gave, "adding as a dual-life module" means forking the CPAN distribution, possibly making some changes (such as normalizing documentation or licensing), and incorporating that fork into the core perl repository. This means that this module will now be installed by default when anyone installs this version of perl.
A dual-lived module is one that is found both in the perl distribution and in its own distribution (on CPAN). For example, Data::Dumper is part of the perl distribution and the Data-Dumper distribution. On the other hand, IPC::Open3 is only available as part of the perl distribution, so it's not dual-lived.
The advantage of a dual-lived module (these and these) is that it can be upgraded without upgrading Perl.
If you wanted to upgrade a core module that isn't dual-lived (these), then you have to upgrade all of Perl.
I frequently use the cpan upgrade command to bring my Perl modules to their latest versions. Regrettably on distributions like CentOS which use ancient versions of Perl it attempts to upgrade perl itself along with other modules like B::X. Is there some way I could combine the ease and power of upgrade but not attempt (and fail) at upgrading core modules? Thank you.
Don't use the system perl. Install your own and start from that. Even when there isn't an ancient perl.
You will have to exclude not just core modules, but also distributions that depend on newer versions of core modules, and distributions that depend on those distributions...
It's a battle you can't win and shouldn't even try to.
BTW, the CPAN-trying-to-upgrade-perl bug was really really ancient; are you really seeing it?
I'm testing my project installation script on CentOS5.5.
My project need Date::Manip module which requires feature module...
When I try to install it (feature) through CPAN, CPAN wants to install Perl 5.9.5...
*** WHOA THERE!!! ***
This is an UNSTABLE DEVELOPMENT release.
The version of this perl5 distribution is 9, that is, odd,
(as opposed to even) and that signifies a development release.
If you want a maintenance release, you want an even-numbered version.
Do ***NOT*** install this into production use.
Data corruption and crashes are possible.
It is most seriously suggested that you do not continue any further
unless you want to help in developing and debugging Perl.
If you *still* want to build perl, you can answer 'y' now,
or pass -Dusedevel to Configure.
How can I handle this kind of problem ?
Date::Manip requires Perl 5.10 to function, see the META.yml:
requires:
...
perl: 5.010
The older version (5.56) instead only requires perl 5.001 to function and should therefore be safe for you to install.
In other words, if you want that latest version you'll have to update your system's perl to at least 5.10. CentOS comes with an old 5.8.8 version, unfortunately.
use feature is a Perl pragma that was first introduced in the 5.10 stable release.
This probably means that Date::Manip requires Perl 5.10.
CPAN is wrong here, don't let it install a development Perl release.
In your specific situation, you can of course go with Perl 5.10 which is the stable version next after 5.9.
In generic situation when there's no later stable version, first you should try to see if the module you want has an older version compatible with your Perl version.
If not, it's a risk/reward trade-off. In a production environment, I'd personally tend to avoid any development branches, unless the success of a critical project hindges on just the module you need AND you can't use another module or roll your own. So far, I never encountered a situation - and can't even concieve of a plausible one - where there's no workaround.
#sebthebert if you want CPAN.pm to only try to install modules that are known to work with your version of perl, see http://cpxxxan.barnyard.co.uk/.
The Centos project provides a version of Date::Manip that works with their version of Perl. It's pre-packaged to work with yum. Currently that seems to be Date::Manip version 5.44 (which predates the requirement for Perl 5.10).
$ sudo yum install perl-Date-Manip
As an aside, are you sure you want to use Date::Manip? DateTime is usually a better choice.