Steven Lembark


Module::FromPerlVer - install modules compatible with the running perl.


    # Aside: unless anyone can find a glaring omission in 
    # the mechanism or utility sub selection this will
    # become version v1.0.

    # ./version directory has sub-dirs with basenames of 
    # parsable perl version strings.
    # when this module is used the highest numbered version
    # directory compatile with the running perl is copied 
    # into the execution directory of Makefile.PL.
    # source_paths() is useful for describing what gets
    # copied, cleanup() is handy for iterating tests or
    # prior to making a bundle.

    # Makefile.PL

    use Module::FromPerlVer;

    # relative paths to files copied for this version of 
    # perl -- different versions of perl may have different
    # collections of files copied.

    my $copied_files    = Module::FromPerlVer->source_paths;

    # remove the files copied and any empty direcories they
    # were copied into (dir's with pre-copy files left in
    # them are untouched).

    my $removed_count   = Module::FromPerlVer->cleanup;

    # at this point lib, t, and friends are populated with 
    # modules compatible with the running perl. because 
    # the destination directory is $Bin this can include 
    # README, MANIFEST, or Changes files. note that 
    # overwriting  Makefile.PL will *not* work since it 
    # has already been compiled.

    # override the perl version:

    # this can be useful for regression testing earlier 
    # versions of modules against the running version 
    # (e.g., validating experimental features).

    $ PERL_VERSION='5.024002' perl Makefile.PL;

    # use a file to determine the perl version.
    # this takes the use-ed version from the file
    # to set the expected perl version (e.g., to 
    # validate if other modules are suitable).

    use Module::FromPerlVer   qw( version_from ./lib/ );

    # or a one-line datafile.
    # "use vX.Y.Z" will find up to that version, "no vX.Y.Z" will 
    # use up to that version minus '0.000001'.
    # perl versions with use or no support any version
    # string avaiable (see "version" module).
    # say that v5.24.2 breaks your module:

    echo 'no v5.24.2' > ./perl-version;

    use Module::FromPerlVer   qw( version_from perl-version );

    # override the source directory:

    # maybe you don't like the name 'version', you
    # prefer "history" instead.

    use Module::FromPerlVer   qw( version_dir history );

    # set up everything but skip making the copy.
    # this reqires callig "copy_source_dir" to get the 
    # versioned files in their proper place.
    # none of the utility subs take any arguments and
    # can all be called using module or object notation.

    use Module::FromPerlVer   qw( no_copy 1 );

    my ( $filz, $dirz ) = Module::FromPerlVer::source_paths;


    my $madness = 'Module::FromPerlVer';



Basic idea: Divide up the source space for a module distro by supporting Perl version. At that point when you want to start using features in a new version of Perl just start a new directory and work with it. When you release the module distro the module's version compatible with the running perl will be selected at install time. No tests in the module for $^V are necessary.

Using the module

Using this module requires two things: The module and a local filesysem labeled by compatible Perl version.

Version Directory

The default directory for module versions is "version". This has sub-directories that are parseable as Perl versions:


in each case the basename of the directory is processed by version::parse.

The filesystem under each version is whatever dir's and files are suitable for that version of perl. Common examples are README, MANIFEST, Changes, ./lib, ./t, ./bin.

Basic Use

Using the module in setup code (e.g., Makefile.PL):

    use Module::FromPerlVer

will look in the ./version directory, sort the subdir's in numerically decreasing order by version (see version) and finds the highest version directory that is less than or equal to the running perl's version. The contents of this directory are copied to the same directory as the running code.

Versions derived from "use" will be less than equal to that version, versions derived from "no" will be less than or equal to the version minus 0.000001.

Supplying the Perl Version

It may be useful in testing to choose a specific subdirectory (e.g., regression testing older code with newer perl executables, or testing the module itself).

Each of these will be passed to version::parse for final validation. If version cannot parse the value then the code will die with a "Bogus perl_version:..." error showing the version string being parsed.

In order of priority the Perl version used to select the module's compatible directory are:


Any true value of will be used. If this is supplied with the "version_from" argument a warning will be issued and the environment variable will be used. Note that "Cat" "Dog" and "I don't know" are all true, but useless and will cause the code to croak.

One use of this is testing the current module with multple versions of perl:


    for perl in /opt/perl5/5*/bin/perl
        for i in version/*
            # pick the appropriate module 
            # version from whatever is running.

            perl Makefile.PL    && 
            make all test       ;

or testing all the available module versions with a specific version of perl:



    for i in ./version/*
        PERL_VERSION="$(basename $i)"   \
        $perl Makefile.PL               &&
        make all test                   ;
use Module::FromPerlVer ( version_from => $path );

The path will be scanned for "use <version string>" and the first one located will be processed. The file can be a module, executable, or flat file with one line in it, so long as "use" followed by a parsable version string is found Life is Good.

The main use of this is validating multiple versions of perl with a specific release of the module.

Overriding "version".

Say you hate the name version:

    use Module::FromPerlVer qw( version_dir history );
Skipping the Copy

If you prefer to call copy_source_dir yourself (e.g., after cleanup or pre-configuring some other part of the environment) use:

    use Module::FromPerlVer qw( no_copy 1 );

This will install all of the utility subs (see "Utility Subs" below) but will not execute copy_source_dir().

Utility Subs

A few utility sub's are installed into Module::FromPerlVer when it is used. These are used internally to drive the file copy process and can be used to supply the values used to build the module filesytem.

None of these take any arguments: they cannot be used to re-set the values determined at import time.

None of them are exported, they can be called usig either package or object notation:

    Module::FromPerlVer::copy_source_dir;   # package::subname

    Module::FromPerlVer->cleanup;           # class->method

None of them exist until import() is called: requiring Module::FromPerlVer will not install any of them.

The only one that is likely useful outside of the module itself are copy_files() and cleanup() which can be called from Perl code for repeated testing (e.g., bash that iterates perl versions).

Calling convention.

All of these ignore any arguments, they can be called as class methods or via fully-qualified paths with the identical effect:


Returns the parsed, numified Perl version value (see version module).


Returns the basename of the version directory (i.e., default 'version').


The subdir from which the files are sourced. This will be a relative path from $FindBin::Bin, including the version directory:


Used in a scalar context this returns an arrayref of relative paths to files copied from the source_dir into the working directory by copy_files().

Used in a list context it returns two arrayrefs: one of the files one of the directories. The former is used with unlink in cleanup to remove only the files that were copied; the latter is used to rmdir empty directories.


Note: Used mainly for testing.

Returns the dest_dir used to copy source_paths.

It mainly allows parallel testing without the tests overwriting one another's output. Might also be useful to install files in a blib directory during testing.


Note: Used mainly for testing.

Returns the source_paths() with the destination directory prefixed. In the default case this will map "./version/X/lib/" to "./lib/". If the dest_dir is, say, a tempdir then the dest paths will look like "./sandbox/10-frobnicate-asdf/lib/".


This executes the copy of all source files into '.'.

Note: If import is called with "no_copy" and a true value then this will have to be called, see examples for calling convention, above.


This first executes an unlink the files, then walks the dir's executing rmdir on the empty ones.

This approach allows for some files to be re-used across multiple releases without getting clobbered by cleanup. Likely examples are common tests (i.e., t/*.t) or a MANIFEST for modules which have all of the same files in each version.



This does the parsing of version numbers from code and dirs. The POD incudes examples of both parsing and sorting Perl versions.


Describes how the files are copied.


This code is licensed under the same terms as Perl-5.26 or any later released version of Perl the user preferrs.


Copyright 2018, Steven Lembark, all rights reserved.


Steven Lembark <>

1 POD Error

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