NO, please don't invoke CPAN in Makefile.PL

It is extremely bad practice. It plays havoc with CPANPLUS based CPAN tester rigs ( like mine ), and for people who don't use CPAN but use CPANPLUS for installing modules.

Update

The best way is to just let CPAN/CPANPLUS deal with installing the module for you as a prereq.

use ExtUtils::MakeMaker;

my %prereqs = ( 
  "Blah::Blah" => 0,
  "Foo::Bar"   => 1.0,
);

eval{require Some::Module};
if ($@) {
    my $reply = prompt("Some::Module not installed. Install (Y/n)", "Y
+");
    $prereqs{"Some::Module"} = 0 unless $reply =~ m/n/i;
}

WriteMakefile(
      PREREQ_PM => \%prereqs,
);
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