What is the difference between require() and include() functions in PHP?

require() and include() are both PHP functions used to include and evaluate external PHP files in a script. However, there is a key difference between these two functions:

require()

require() is used to include a specified file in the script, and if the file is not found or cannot be included for any reason, it will produce a fatal error and halt the script execution.

include()

include(), on the other hand, is used to include a specified file in the script, and if the file is not found or cannot be included, it will produce a warning and allow the script execution to continue.

Therefore, the main difference between require() and include() is how they handle errors when the included file is not found or cannot be included. While require() is more strict and halts the script execution, include() is more lenient and allows the script to continue running.