I'm new with Perl and stumbled on a doubled modules installation.
I made a fresh installation of Strawbery Perl on Windows 10. After that, I tried to update all modules at once by using a command proposed in this answer; :
cpan-outdated -p | cpanm
Unfortunately, it appeared that probably the updates were installed on another location:
whichpm -a Mojolicious
C:\Strawberry\perl\site\lib\Mojolicious.pm
C:\Strawberry\perl\vendor\lib\Mojolicious.pm
whichpm -v Mojolicious
whichpm: WARNING: DUPLICATE module files found for 'Mojolicious':
C:\Strawberry\perl\vendor\lib\Mojolicious.pm
Mojolicious 8.22 (non-core) C:\Strawberry\perl\site\lib\Mojolicious.pm
How to deal whit that case?
How to prevent such cases in further updates?
perl -wE "say for @INC"
C:/Strawberry/perl/site/lib/MSWin32-x64-multi-thread
C:/Strawberry/perl/site/lib
C:/Strawberry/perl/vendor/lib
C:/Strawberry/perl/lib
Everything is working as expected.
There are three sets of installation locations: core, vendor and site.
The vendor directories are usually used by the package managers of linux distros, but it appears that Strawberry Perl includes a number of non-core modules in its distribution (including Mojolicious) and it places these in the vendor directories. This is proper.[1]
The site directories are used for user-installed modules. So your upgraded Mojolicious was installed into the site directories. This is proper.
(More on the differences here.)
This is not a problem because the site directories are placed before the vendor directories in @INC, so the user-installed version of a module is found before the vendor-installed version.