Module::CoreList contains the hash of hashes %Module::CoreList::version, this is keyed on perl version as indicated in $]. The second level hash is module => version pairs. . Note, it is possible for the version of a module to be unspecified, whereby the value is undef, so use exists $version{$foo}{$bar} if that's what you're testing for. . It also contains %Module::CoreList::released hash, which has ISO formatted versions of the release dates, as gleaned from perlhist. . New, in 1.96 is also the %Module::CoreList::families hash, which clusters known perl releases by their major versions.