Introduction to Cgi/Perl: Getting Started With Web Scripts [Paperback]

Steven E. Brenner (Author), Edwin Aoki (Author)

Book Description

Publication Date: December 1995

This guide provides information on everything users need to know to create customized dynamic programs for the World Wide Web using Perl and the Common Gateway Interface (CGI). It reviews the communication technologies required to present an HTML page from either a static file or a script.

Editorial Reviews

Amazon.com Review

An important guide for developing dynamic content and forms to add impact and interaction to Web sites. Brenner is the author of cgi-lib.pl, the de facto standard library for creating CGI scripts with Perl. Used for everything from NASA space data to Byte Magazine's on-line comment box, this library makes CGI scripting intuitive and fun.

If you want to see an excerpt from this book, look below, or click on the title.

Excerpt. © Reprinted by permission. All rights reserved.

The following is a short essay from the book for recognizing scripts.

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Recognizing a Script When You See It

How does a server tell that a CGI script is a script and not a document file? Often, without some help from the script writer, it can't. In fact, one of the most common errors encountered by CGI programmers is the failure to provide the hints necessary for the server to make this distinction. A confused server may generate a variety of different errors, depending upon how the server is configured and how the script was called. The most common result is that the text of the script (i.e., its source code, as in Listing 1.2) is output, rather than the result of its execution. You might also receive errors like "can't POST to non-script"- this message is particularly infuriating because posting to a script is exactly what you are trying to do.

These problems arise because there are no set standards for how a server should recognize a CGI script; consequently, different servers work in different ways. A model used by both the NCSA and CERN servers is to have a special directory in which all scripts (and only scripts) reside. The actual location of the directory on the disk and the name by which it is accessed over the Web (typically /cgi-bin) are specified in configuration files. Any request for a document in that directory or its subdirectories is treated as a request to execute that document as a script. Most servers support this model.

A newer approach is to use a filename extension to recognize CGI scripts, mirroring the technique used to determine a file's Media Type. The precise extension (and indeed the ability to have the extension specify a CGI script) is typically defined as part of the server's configuration. The most common extension for scripts is .cgi, though most Windows servers use the extensions .exe or .pl, and recent versions of Macintosh servers have used .acgi.

The use of extensions means that the CGI scripts can reside anywhere in the server's directory space, which has benefits and drawbacks. On the plus side, it means that scripts can be kept in intuitive locations, near related HTML files and other documents. On the minus side, spreading scripts all over the directory hierarchy makes it harder to keep track of all of them, in case they need to be updated. More importantly, if the server is configured to allow access to documents in users' personal directories (typically by mapping URLs with ~username to ~username/public_html), anyone can create and execute their own CGI scripts. While this may be appealing, it is common for inexperienced users to inadvertently write CGI programs with major security holes (especially if using shell scripts). Thus, a single user can potentially jeopardize the security of an entire server computer.

For these reasons, many servers come with extension-based CGI script recognition disabled by default. Even if enabled, many Internet service providers explicitly prohibit CGI scripts in users' space to avoid security hassles. If you try to run a CGI script in an area of the server where their use is not permitted, you may receive an access denied error. This message can be confusing as it also appears when a file's permissions are set incorrectly. Refer to Appendix A for additional troubleshooting hints.

Only a server can interact with a script. A client program cannot directly run (e.g., with the "open file" command) a CGI script; if asked to do so, the browser will likely display the script's source code. Because CGI communications take place between a server and a script, every CGI interaction must involve an HTTP server.

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More information can be found at www.mispress.com/introcgi/ the Online Appendix to the book. While this Online Appendix was especially designed to complement the book, it can serve as a useful resource for anyone interested in CGI and Perl. In addition to current information about CGI, Perl, and the Web, you can also find downloadable code, pointers to the Perl distribution, and links to other helpful sites. It also has a mirror of the homepage for cgi-lib.pl, the de facto standard library for creating CGI scripts with Perl.

Product Details

• Paperback: 151 pages
• Publisher: M & T Books (December 1995)
• Language: English
• ISBN-10: 1558514783
• ISBN-13: 978-1558514782
• Product Dimensions: 9.2 x 7.1 x 0.5 inches
• Shipping Weight: 11.2 ounces
• Average Customer Review: 4.6 out of 5 stars  See all reviews (9 customer reviews)
• Amazon Best Sellers Rank: #2,529,559 in Books (See Top 100 in Books)

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10 of 10 people found the following review helpful:

4.0 out of 5 stars A Good Introduction... Not a Tutorial, February 15, 1999

By A Customer

This review is from: Introduction to Cgi/Perl: Getting Started With Web Scripts (Paperback)

If you are bright, and you want to understand the concept of Perl, this book will get you started. You probably will not come away able to write any programs, although you will gain some tools for doing so. I have not yet found a single book to get people started with Perl, but a combination of this book, "Learning Perl" and "The Perl CGI Cookbook" makes a good beginner library.

3 of 3 people found the following review helpful:

5.0 out of 5 stars A great Intro to Perl!, May 15, 1999

By A Customer

This review is from: Introduction to Cgi/Perl: Getting Started With Web Scripts (Paperback)

I thought this book was excellent, it was a little short, but still good. My actual rating would be 4.5 stars, this is because once it gets into chapter 3 pretty deep, I lost my self and had to read it over a couple times, and instead of using cgi-lib.pl, I'd rather know how to do it from scratch.

Overall though a great book! c'ya

3 of 3 people found the following review helpful:

5.0 out of 5 stars Just what it implies: INTRO to CGI/PERL, August 5, 1997

By A Customer

This review is from: Introduction to Cgi/Perl: Getting Started With Web Scripts (Paperback)

If your looking for a mammoth manual or encyclopedic guide to CGI and PERL, then you've come to the wrong place. This 150 page primer gets you off and running writing your own Perl scripts in the easiest way. Many examples and exercises aim your learning to integrating your knowledge into hypertext web pages. Receiving user input and producing valid output with CGI, HTML forms elements; all explained in an easy to follow, step by step text. Highly recommended to anyone who wishes to gain a basic understanding of the Perl scripting language