This section describes how to include script code from other files by using the do() function, or the require() function.
There are many reasons for including script code from other files. One of them
is that you have a section of code that is identical to many of your script files,
and you don't want to copy it to each of your script files. Examples of this type
of shared code are default values of controlling variables and common subroutines.
There are two simple ways to include source code from other files:
1. Using do() function to include and execute the source code of the specified file.
It will search the file in the @INC path name array.
It will add an entry to %INC with file name as key and full path name as value.
It will return the last expression executed. So to make the calling program happy, you should
put a dummy expression like "1;" at the end of the include file.
2. Using require() function to include and execute the source code of the specified file.
require() will do everything do() does, and is smarter than do() in the following areas:
It will check %INC to see if the specified file has already being include. If so,
do nothing and return 1. Otherwise, continue.
It will add an entry to %INC with file name as key and full path name as value, only
if the execution was successful.
