Man pages matching name ipc::pubsub in section 3pm:

IPC::PubSub.3pm.en	debian 10 / libipc-pubsub-perl
IPC::PubSub.3pm.en	debian 11 / libipc-pubsub-perl
IPC::PubSub.3pm.en	debian 12 / libipc-pubsub-perl