Almost all the libraries you deal with are in-house. Which is part of what I'm pointing out, most of getting up to speed in any company is learning about their domain-specific codebase, not the language they happen to be using.
You're certainly at an advantage if you know some of those things already, that goes without saying. I'm just pointing out that many people seem to overestimate the impact of the programming language on the overall stack. Knowing DB workflows, distributed programming etc. is much more important than knowing language trivia which you can mostly trivially look up.
My point was, to take a simple example, at places like Booking.com [new] people will typically find out about the used CPAN Date classes from the code or their table neighbour. Not by rolling their own or crawling all of the CPAN before finding DateTime.
But sure, the internal code will be a bigger issue.
You're certainly at an advantage if you know some of those things already, that goes without saying. I'm just pointing out that many people seem to overestimate the impact of the programming language on the overall stack. Knowing DB workflows, distributed programming etc. is much more important than knowing language trivia which you can mostly trivially look up.