a perl book. (and yes, modern perl[1] is still a good, viable candidate for up-to-date-best-practices development. the only downside is it takes a certain amount of discipline to get it right. The other possible downside is that perl is currently not trendy, on the other hand it's proven to be a very good performer in the long game).
[1] http://modernperlbooks.com/books/modern_perl_2016/ - not my book, mine was more specialised, and I'm not going to transparently disclose my identity here :).