What are the differences between library() and require() when loading a package?

Both point ?libraryto ?requierethe same help. They both do the same thing: they load a certain package into the active session. The difference between the two is detailed in the help:

library(package) and require(package) both load the namespace of the package with name package and attach 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

Basically:

require():

• Returns FALSEand issues a warningin case of not being able to load the package
• Does not stop the eventual execution of the script
• The console shows, apart from the possible package messages, the text Loading required package: <paquete>that can be eliminated by means ofquietly = TRUE

library():

• Issues a errorin case of not being able to load the package
• By default it does not return any value, unless we use the parameterlogical.return = TRUE
• Stops script execution

The use of require()over library()is a bit vague, normally the packages are loaded at the beginning of a script and it is logical that if it cannot be loaded the execution is not continued, so it library()would be the appropriate option, on the other hand we could eventually find ourselves with these scenarios:

• Try to load a package and in case of error use another one with similar functionality

• Try to load a package and in case of error try to install it, for example:

  if (!require(package, character.only=T, quietly=T)) {
      install.packages(package)
      library(package, character.only=T)
  }
  

For these cases the use of require()would be justified since the execution is not stopped.

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