G'day LittleJack,

From your post yesterday (Starting out with Dancer and falling at the first hurdle) you're using Dancer2. The link you've provided is for Dancer documentation; the Dancer2 equivalent is https://metacpan.org/dist/Dancer2/view/lib/Dancer2/Manual/Deployment.pod#With-Plack. I had a quick look and can't see any substantial differences; however, it's better to use the right version of the documentation.

"Which perl and which libraries is my Apache (2.4.7) trying to use?"

Either modify your app.psgi, or write a new one, which outputs various version (and perhaps other) information. A very rough, command line example:

$ perl -e '
    use List::Util;
    print "Perl version: $]\n";
    print "List::Util version: $List::Util::VERSION\n";
'
Perl version: 5.034000
List::Util version: 1.56
[download]

Other suggestions:

• Check in your Apache logs for some hints.
• Check which version of mod_perl or mod_perl2 you have installed.
• Do you have any instances of Apache::* that should be Apache2::*.
• Specify a minimum Perl version; e.g. 'use 5.020;'.
  • The first version of perldoc which mentions 'pairmap' and 'pairgrep' is for Perl v5.20: https://perldoc.perl.org/5.20.0/List::Util.
• Specify a minimum List::Util version; e.g. 'use List::Util 1.29 qw{...};'.
  • See https://metacpan.org/dist/Scalar-List-Utils/changes which indicates 'pairmap' and 'pairgrep' were introduced in v1.28 (with a bug) and fixed in v1.29.

Note that I'm attempting to guess what your app.psgi and Apache config look like. Something more concrete from you would be helpful.

The first version of perldoc which mentions 'pairmap' and 'pairgrep' is for Perl v5.20

Well that might explain it because my default Perl is still on 5.18.

But when I check my $List::Util::VERSION it's 1.62 so it should be fine.

The mystery is somewhat solved when I use Apache2::Status, because Apache is loading some modules from /usr/local/lib/perl/5.18.2/ but some others from /usr/lib/perl/5.18/ where there is indeed an old List::Util.

How do I convince Apache to load a newer one from a different directory?

See Adjusting @INC from the fine documentation.

---

🦛

Which perl and which libraries is my Apache (2.4.7) trying to use?

You can find out via the highly configurable Apache2::Status handler.