PHP: One large file or several small files

Question

I self taught myself PHP, so I don't know many of the advantages and disadvantages in programming styles. Recently, I have been looking at large PHP projects, like webERP, Wordpress, Drupal, etc and I have notices they all have a main PHP page that is very large (1000+ lines of code) performing many different functions. Whereas, my projects' pages all seem to be very specific in function and are usually less than 1000 lines. What is the reasoning behind the large page, and are there any advantages over smaller more specific pages?

Thanks for the information.

Answer 1

It's partly about style and partly about readability/relationships. Ideally everything in a single file is related (ex. a class, related operation functions etc.) and unrelated items belong in another file.

Obviously if you are writing something to be included by others making a single file can have its advantages. Such as a condensed version of jQuery, etc.