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Editorial Team
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Asked: 2026-05-17T22:16:29+00:00

I want to install File::Fetch, which is a core module in Perl 5.12, in

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I want to install File::Fetch, which is a core module in Perl 5.12, in my Perl 5.8.9. In general, I want to compile and install future-dated modules in my back-dated Perl because I cannot upgrade my Perl.

So I downloaded the module and also its dependencies. It’s quite painful following the dependency tree but I’m more concerned about the fact that some of them are core modules. If I install these, my Perl 5.8.9 core will have patches from 5.12.

My question is how I can know whether I can safely install the future-dated modules, especially the core modules. Is there a tutorial for this purpose of testing backwardcompatability in Perl?

EDIT:
My module is dual lifed, but I cannot compile it using cpan. It said my FTPsite.yaml has a bad element. However, I followed the dependencies in the modules’ META files, and I could compiled the module. Is this one of the odd bits with cpan? Thank you.

I cannot recreate the issue after I installed all those dependencies manually. But here is the error:

cpan[5]> install File::Fetch
Running install for module 'File::Fetch'
Running make for B/BI/BINGOS/File-Fetch-0.24.tar.gz
CPAN: Digest::SHA loaded ok (v5.48)
CPAN: Time::HiRes loaded ok (v1.9715)
CPAN: YAML loaded ok (v0.72)
Alert: While trying to 'parse' YAML file
 '/Users/martin/.cpan/FTPstats.yml'
with 'YAML' the following error was encountered:
  YAML Error: Invalid element in map
   Code: YAML_LOAD_ERR_BAD_MAP_ELEMENT
   Line: 3
   Document: 1
 at /opt/local/lib/perl5/site_perl/5.8.9/YAML.pm line 36
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1 Answer

  1. Editorial Team

    If the module is available separately (i.e. “dual-lifed”), as both a standalone distribution and inside core Perl, then the standalone version is safe to install on an earlier Perl, assuming its Makefile allows it. That is, if you can do cpan <Module> and it builds and tests without errors, then you are good.

    The only problem is if a module is not dual-lifed, which I opined about in this question — which is where you are likely S.O.L.

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