O'Reilly -- News -- Why Learn CGI?

CGI was the first, widely used system for creating dynamic content on the web. Prior to CGI (Common Gateway Interface), the only way to create dynamic content was to write a customized web server. That's not easy, of course, so few people bothered. CGI, however, allowed developers to connect separate programs to the web and thus transformed it from a repository of static documents and images into a network of online applications.

Today, there are numerous technologies available for creating dynamic content. Alternatives to CGI include the following:

Java Servlets

Allaire ColdFusion

Active Server Pages (ASP)

PHP

mod_perl

With the increased use of these newer technologies, it is not uncommon for someone to ask whether CGI is still relevant today. Indeed, some of the companies marketing these newer technologies have a habit of referring to CGI applications as legacy applications, inspiring images of dusty mainframes.

Will CGI development soon be as obsolete as COBOL? Well, don't believe everything you read, especially if it was written by a marketing department. One of the virtues of CGI is that it is an open standard that does not have a company or even a group of volunteers to promote it. Thus, it is an easy target, and its dominating market share makes it a popular target as well.

So for the person who asks, "Why should I learn CGI?" I offer the following reasons:

CGI remains the most popular way to develop dynamic content. More dynamic pages are created on the web today with CGI than with any other technology, and companies continue to develop new applications with CGI.

CGI is universal. CGI is supported by all the major web servers as part of the default installation. Some Java web servers even support CGI via a compatibility mode.

CGI is language independent. Although Perl is certainly the most popular language for developing CGI scripts, CGI allows you to develop in any language. The more popular alternatives to Perl include C, Python, and Unix shell scripts; but you can also write CGI scripts in Visual Basic, AppleScript, and even Java.

CGI was intentionally designed as a lightweight interface over HTTP. Thus, learning CGI helps you better understand HTTP, which is the foundation for all web transactions, regardless of language or interface. Time spent learning CGI is an investment, not a loss.

Numerous ISPs and homepage services allow CGI scripts. Some, like Hypermart, offer this service for free. Thus, developers can learn CGI authoring without paying a penny. And a site with CGI scripts can be hosted without resorting to more expensive options like a leased line or colocation.

The basics of CGI are intuitive and easy for programmers to understand. CGI typically uses standard input and output streams and environment variables. This interface is the same as that used by Unix shells and the DOS command prompt. Perl, incidentally, was originally written for the Unix shell environment, which is one reason why Perl works so well for CGI scripting.

There is a great wealth of CGI resources online. Because CGI has been around for a while, there are a great deal of online resources available for CGI authors, including sample CGI scripts and libraries/modules. Most of this code is available for Perl because of Perl's popularity as a language for CGI and because Perl developers have a tradition of sharing code with each other. The best source for Perl code is CPAN.

In closing, there is no reason why you should learn only one web development technology. If you want to become an effective and successful web developer, it is valuable to learn a few. And, for the reasons I've outlined above, if you are going to learn more than one technology, the first should be CGI--especially given its popularity.

Scott Guelich graduated from Oberlin College in 1993 with a philosophy degree and decided to "only take a few years off" before continuing with graduate school. Unable to find any listing for "Philosopher Wanted" in the classifieds, and having done some programming while growing up, he quickly found himself working with computers. He discovered the Internet the following year and Perl the year after that. He has been doing web development for four years and currently works as a consultant in the San Francisco Bay Area. Nonetheless, he insists that he may still make it back to graduate school...some day.