Core PHP Programming: Using PHP to Build Dynamic Web Sites

The include and require Functions

The include and require functions take the path to a file. The file is parsed as if it were a stand-alone PHP script. This is similar to the include directive in C and the require directive in Perl. There is a subtle difference between the two functions. When the require function is processed, it is replaced with the file it points to. The include function acts more like a function call.

The difference is most dramatic inside a loop. Imagine having three files you wanted to execute one after the other. You could put an include inside a for loop, and if the files were named something like include1.php, include2.php, and include3.php, you would have no problem. You could just build the name based on a counter variable. ...