But you've over-ridden that by using cpanm with the system perl, no? That way lies madness and despair. Keep the system perl and cpanm completely separated to avoid this particular brand of infernal torment.

Find out where cpanm has installed its versions (hopefully not in the vendor tree) and clear out everything that was added in your last change - perllocal.pod should help with that.

I probably have mixed system perl with CPAN... Can anyone point at a guide on how to properly install and maintain perl (and avoid compatibility issues between CPAN and vendor distros)?

In my case, the system uses perl for dependencies (e.g. munin and nagios) and I add modules not available in the system distro (e.g. yum) via CPAN.

It would be good to have everything relating to the Dancer2 app separate. I would then be able to backup the app and all the perl modules it relies on together.

It isn't obvious to me how to do that though, since @INC contains both cpan and vendor perl and it seems all too easy to mix the two.

Mixing the OS-installed (vendor installed) modules and the fresh distributed modules could cause problems in any languages environment.

Therefore myself using the anyenv for all my needs. The installation is straightforward:

$ git clone https://github.com/riywo/anyenv ~/.anyenv
$ echo 'export PATH="$HOME/.anyenv/bin:$PATH"' >> ~/.your_profile
$ echo 'eval "$(anyenv init -)"' >> ~/.your_profile
$ exec $SHELL -l
[download]

After you got installed the anyenv, you could install many different language environments, like plenv for the perl.

$ anyenv install plenv
[download]

and now you could install (compile) any perl version what exists in the repository

$ plenv install -l #to show installable perl versions
$ plenv install 5.24.0 #install the 5.24.0
$ plenv global 5.24.0 #set the 5.24.0 as default perl for you
[download]

Read more at plenv github page

Also, you probably will want to change all #!shebang lines, from

#!/usr/bin/perl
to
#!/usr/bin/env perl
[download]

perlbrew would be one option.