Distinguishing require, include, require_once, and include_once

In PHP, the usage of these functions can be confusing, leading to questions like:

• When to choose require over include?
• When to use require_once vs. require?

require vs. include

Both functions embed external PHP scripts into the current one. However, they handle errors differently. If an error occurs, include generates a warning and continues execution; require generates a fatal error and stops the script.

require_once vs. require

In essence, they are identical, except that require_once checks if a file has already been included and skips its inclusion if true.

Re-evaluating require_once and include_once

While these functions may have been useful in the past, their relevance has diminished due to caching mechanisms employed by opcode caches. If you find yourself using *_once variants, consider restructuring your code for clarity and efficiency.