What is the difference between require() and library()?

Question

What is the difference between require() and library()?

Answer 1

?library

and you will see:

library(package) and require(package) both load the package with name package and put it on the search list. require is designed for use inside other functions; it returns FALSE and gives a warning (rather than an error as library() does by default) if the package does not exist. Both functions check and update the list of currently loaded packages and do not reload a package which is already loaded. (If you want to reload such a package, call detach(unload = TRUE) or unloadNamespace first.) If you want to load a package without putting it on the search list, use requireNamespace.