What was Pip's Christian name in Great Expectations? How did he come to be known as Pip?

Pip's Christian name, as we learn in the first line of the novel, is Philip Pirrip. He comes to be called Pip because his preschool self (he says his "infant" self, but, in this context, "infant" means under five years old) could not easily pronounce the name Philip Pirrip. He started calling himself Pip, as that was easier to say, and the nickname stuck. As his full name almost never comes up again after the start of the novel, it can be easy to forget.
We learn too that Pip has no memory of his parents, whom he says he never "saw." This suggest that they both must have died shortly after his birth. He is named after his father and now lives with his much older sister, Mrs. Joe Gargery.