Writing CGI Applications with Perl - Preface
Purpose of this Book
Perl's popularity as a CGI scripting language is growing by leaps
and bounds. However, there are few books available today that
cover this subject in depth including a broad range of concepts. We wanted our book to help people learn to
use Perl and convince them that it is the best choice for their Web-based applications. The goal of this book
is not to teach the Perl language--although certain tricks and features may be learned--but to show how
Perl can accomplish the tasks needed for many of today's online applications. In short, we wanted to
provide a resource that not only teaches new uses of Perl but challenges the reader with exercises that use
the concepts. Standard Perl documentation is also provided. The book covers a wide range of concepts, and
using these, you should be able to write almost any Perl/CGI application with the techniques provided.
This book is different from others about Perl and CGI. It takes a cumulative approach and introduces
applications that use concepts learned in previous chapters. Each chapter will cover at least one specific
Web-based application and explain the code line by line (or block by block) so you not only learn what the
scripts are doing but how they are doing it. And in order to help induce self-learning and application building,
each application is working but incomplete. We provide skeleton applications that can stand on their own,
but we leave out certain features that can be added (and we suggest adding them in the exercises) using the
information in that chapter and in previous chapters. Our goal is not to give you "cut and paste" software but
rather to show you how to write the software yourself.
Chapter 1, Perl, CGI, and this Book. This chapter explains what Perl and CGI are. It also supplies more
detail about this book and shows how to use the CPAN module.
Chapter 2, What You Should Know. We don't expect the reader to know everything, but we do expect at least
a base level of knowledge. This chapter outlines what you should already know and explains a few things
that you may not already know but should to get the most out of this book, such as tainting, security
concerns, and troubleshooting.
Chapter 3, Using Your Environment. Many times in CGI applications you need information from the client,
such as IP address or browser information. This chapter covers how to access the Web server environment
variables and what they mean.
Chapter 4, Introduction to Web Forms. There are few online applications where there is not some sort of
Web form used to allow an end user to submit information. Chapter 4 explains the HTML elements of
creating a Web form, as well as how to obtain the user input.
Chapter 5, Working with Cookies. Using cookies to store data on a Web client can be very useful to record
Chapter 6, Access Counters. Many people want to count how many people come to their Web site. The
examples in this chapter show you how to do this.
Chapter 7, Web-Based File Uploading. Here you will learn how to safely allow end users to upload files to a
server from their local hard drives.
Chapter 8, Tracking Clicks. It can sometimes be useful to know what links on a Web site are being followed
and from where. The examples in this chapter show how to track these clicks.
Chapter 9, Using mod_perl. The popular mod_perl Apache module can be extremely useful when it is
appropriate for an application. You will see how to configure mod_perl, as well as how to use and write
mod_perl Perl modules.
Chapter 10, Web-Based E-mail. The examples in this chapter demonstrate how to connect to a POP3
server to view e-mail, view attachments, and send e-mail via the Web.
Chapter 11, Introduction to DBI and Databases on the Web. Chapters 1-10 presented basic uses for
database connectivity in previous examples. This chapter examines the Perl DBI in more depth.
Chapter 12, Tied Variables. The magic of tying data structures to variables and how to do this when the data
structure is a database is explained in this chapter.
Chapter 13, Embedding Perl in HTML with Mason. This popular tool is examined and explained. This
chapter shows you how to embed Perl within HTML and use the HTML::Mason module to speed up
development and maintenance time.
Chapter 14, Document Management via the Web. By now you will have learned how to upload files to a
server. This chapter shows you how to manage your files remotely via the Web.
Chapter 15, Dynamically Manipulating Images. Creating charts, graphs, thumbnails, and galleries, and
changing images on the fly are all concepts that can be useful in CGI applications. This chapter shows you
how to add these techniques to your software.
Chapter 16, RSS and XML. XML is another tool that is gaining in use and popularity. This chapter shows you
how to use both XML and a derivative of it, RSS and RDF, to share information and use in applications.
Appendix A, Server Codes. Learn what the codes returned by a Web server mean.
Appendix B, Environment Variables. This is a list of the most common Web server environment variables.
Appendix C, POSIX::strftime() Formats. This book uses the POSIX module a few times to format date
strings. This list shows the formats that the module uses and what the formats do.
Appendix D, General Public License. If you didn't read the copy that came with Perl, you can do so here.
Appendix E, Artistic License. Another license under which Perl is distributed.
Appendix F, Perl Documentation. A list of the documentation that comes with Perl. This list is useful for
interactive learning along with this book.
Appendix G, ASCII Codes. A list of ASCII, hex, and decimal codes.
Appendix H, Special HTML Characters. A list of special characters, such as £, ®, and Æ. Although these
aren't specific to Perl, you will probably need some of them sooner or later when generating HTML with
One of the best resources for Perl is the Perl documentation and the documentation included in various Perl
modules. Chapter 1 covers how to read this documentation with the perldoc command. The Perl homepage at
http://www.perl.com is extremely useful with articles, tips, documentation, other resource links, and what's
new in the world of Perl. The Perl Mongers homepage at http://www.perl.org supplies good information on
the world of Perl and Perl advocacy. The use Perl Web site at http://use.perl.org is a community page where
Perl information is shared and discussed. The Perl Documentation Web site at http://www.perldoc.com is a
very useful site containing the latest Perl documentation. Finally, the Perl Monks at
http://www.perlmonks.com is another community where people can ask questions, answer questions, chat,
and share knowledge.
Usenet has Perl newsgroups that are also useful: comp.lang.perl.announce has Perl announcements;
comp.lang.perl.misc is a high traffic list for asking Perl-related questions; and comp.lang.perl.modules
announces and discusses Perl modules. A non-Perl-specific news group that deals with CGI is
comp.infosystems.www.authoring.cgi. Here you can discuss all topics CGI.
We would love to hear from you. You can find information on this book and errata at
http://www.perlcgi-book.com and http://www.awl.com