[nbm]

As far as I know, at Facebook we don't give pre-emptively/usually give people a book to learn PHP. Those that don't know PHP (or are rusty) can generally get the syntax/keywords right in an hour, and then there's a longer time spent getting familiar with both the standard library and our own frameworks/libraries.

There is a lot of good code to look at and learn from, and the Bootcamp program teaches a bunch of our own library and some guidance on what good and bad standard library functions are for certain cases. We also have a "newbie" group where people can ask questions about the codebase. And if you do something without knowledge of a built-in (or Facebook) function/class and make things more complex than they need to be, your code reviewer will let you know how to do it easier/more idiomatically. Every once in a while there are language tech talks, and sometimes even whole-day training sessions (we did one on exciting new C++11 features).

Besides that, I definitely spent a lot of my time with php.net/function_name open and exploring when I couldn't remember all the functions available or the parameters and order.