Decoding CGI: A Comprehensive Guide

Understanding CGI and Its Functions

CGI is typically used in conjunction with standard HTML tags to collect data from a user, which is then passed to a CGI routine for processing. Some of the most common applications of CGI include:

• Guestbooks: The CGI routine validates the data, sends an email acknowledgment to the writer, possibly notifies the webmaster, and creates the guestbook entry.
• Email Forms: A basic CGI forms routine formats the data into an email and sends it to the webmaster. More complex routines can manage a database, send acknowledgments, and validate data.
• Mailing List Maintenance: These routines allow visitors to subscribe and unsubscribe from a mailing list. The CGI routine maintains a database of email addresses, and the more advanced ones send acknowledgments to the visitor and webmaster.

CGI Languages: PERL and Others

A CGI routine can be written in any language that understands the CGI standard. One popular CGI language is PERL, a scripting language that is relatively easy to understand and use. Unlike compiled languages like C++ or Visual Basic, which can be directly executed, a PERL routine must be interpreted by the web server each time it is run.

The CGI Process Simplified

Here's a simplified explanation of how CGI works:

• As a webmaster, you specify a form tag that includes the name of the CGI routine.
• You create HTML tags to collect data from your visitors.
• Each input tag includes a variable name. The data collected from the visitor is stored in this variable.
• When the visitor clicks the "submit" button, the specified CGI routine is executed. The browser essentially waits for it to complete.
• The CGI routine retrieves the data from the variable names and performs the necessary actions.
• Once the CGI routine is finished, control is returned to the web client (the browser).

Important Considerations for CGI Routines

• If your host allows it, you can install CGI routines on your own site. For example, Addr.Com is a web host that allows for CGI routines. Some web hosts provide pre-written routines if you can't install your own. If these don't meet your needs, you can use a remote hosting service.
• If you install your own routines, they usually need to be installed in the cgi-bin directory of your site. This is a special location that allows scripts and programs to be executed.
• CGI routines work best on Apache-style servers. While Windows NT and Windows 2000 do support CGI, it can be slow and problematic.
• If you use a remote hosting service, remember that they may display advertisements or redirect visitors away from your site.
• When writing a CGI routine, you can choose a scripting language like PERL or a compiled language like C++ or Visual Basic. Any language that can execute on the web server is acceptable.

This introduction to CGI should help clear up some of the mystery surrounding this important web technology.