require() Function - Including Script Files

This section provides a tutorial example showing you how to the require() function is better than the do() function - if the same file is included multiple time, the require() function will only execute it once.

As mentioned in the previous section, require() function can be used to include script code from another file into the current script file. To try this out, I wrote another include file, MyRequireLib.inc,

#- MyRequireLib.inc
#- Copyright (c) 1995 by Dr. Herong Yang, http://www.herongyang.com/
#
   $author = "Dr. Herong Yang";
   print("Printing from MyRequireLib.inc...\n");
sub myRequireSub {
   print("Printing from myRequireSub()...\n");
}
1;

Here is tutorial script that tests the difference between the do() function and the require() function:

#- IncRequireTest.pl
#- Copyright (c) 1995 by Dr. Herong Yang, http://www.herongyang.com/
#
   print("\nTesting require()...\n");
   require("MyRequireLib.inc");
   require("MyRequireLib.inc");
   print("Author = $author\n");
   &myRequireSub();

   print("\nTesting do()...\n");
   do("MyDoLib.inc");
   do("MyDoLib.inc");
   print("Author = $author\n");
   &myDoSub();
   exit;

The output matches my expectation. The second require() call didn't do any execution.

Testing require()...
Printing from MyRequireLib.inc...
Author = Dr. Herong Yang, http://www.herongyang.com/
Printing from myRequireSub()...

Testing do()...
Printing from MyDoLib.inc...
Printing from MyDoLib.inc...
Author = Herong Yang
Printing from myDoSub()...

Table of Contents

 About This Book

 Perl on Linux Systems

 ActivePerl on Windows Systems

 Data Types: Values and Variables

 Expressions, Operations and Simple Statements

 User Defined Subroutines

 Perl Built-in Debugger

Name Spaces and Perl Module Files

 Including Script Codes from Other Files

 do() Function - Including Script Files

require() Function - Including Script Files

 "package" Statement - Switching Name Space

 BEGIN(), CHECK(), INIT() and END() Functions

 Defining Your Own Perl Module

 CalendarModule.pm - A Sample Perl Module

 Symbolic (or Soft) References

 Hard References - Addresses of Memory Objects

 Objects (or References) and Classes (or Packages)

 Typeglob and Importing Identifiers from Other Packages

 String Built-in Functions and Performance

 File Handles and Data Input/Output

 Open Files in Binary Mode

 Open Directories and Read File Names

 File System Functions and Operations

 Converting Perl Script to Executable Binary

 Using DBM Database Files

 Using MySQL Database Server

 Socket Communication Over the Internet

 XML::Simple Module - XML Parser and Generator

 XML Communication Model

 SOAP::Lite - SOAP Server-Client Communication Module

 Perl Programs as IIS Server CGI Scripts

 CGI (Common Gateway Interface)

 XML-RPC - Remote Procedure Call with XML and HTTP

 RPC::XML - Perl Implementation of XML-RPC

 Integrating Perl with Apache Web Server

 CGI.pm Module for Building Web Pages

 LWP::UserAgent and Web Site Testing

 References

 PDF Printing Version