gistfile1.txt

#!/usr/bin/perl
# Usage: upgrade-cpan.pl 5.14.0 | sort -u > /tmp/modules.txt
use strict;
use File::Find::Rule;
use JSON;

my $old = shift;

my @files = File::Find::Rule->file->name('install.json')->in("$ENV{HOME}/perl5/perlbrew/perls/perl-$old/lib/site_perl/$old");
for my $file (@files) {
    my $module = parse_json($file)->{module};
    print $module, "\n" if $module;
}

sub parse_json {
    open my $fh, shift or die $!;
    JSON::decode_json(join '', <$fh>);
}

Replacing $ENV{HOME} with $ENV{PERLBREW_ROOT} will support perlbrew installs in non-standard locations.