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CGI Programming with Perl By Scott Guelich, Shishir Gundavaram and Gunther Birznieks, Second Edition, published July 2000. The first edition of CGI Programming on the World Wide Web was published in early 1996. Because CGI has changed so much in the last few years, it is only appropriate that this new edition reflect the changes. Thus, most of this book has been rewritten. New topics include CGI.pm, HTML templates, security, JavaScript, XML, search engines, style suggestions, and compatible, high-performance alternatives to CGI. Previous topics, such as session management, email, dynamic images, and relational databases, have been expanded and updated. Finally, we modified our presentation of CGI to begin with a discussion of HTTP, the underlying language of the Web. An understanding of HTTP provides a foundation for a more thorough understanding of CGI. What is CGI? As stated by the name, Common Gateway Interface, CGI is an interface, a developing environment or context. it is essentially the minimum that the web server needs to provide in order to allow external processes to create web pages. When a web server gets a request for a CGI script, the web server executes the CGI script as another process ( i.e., a separate application ); the server passes this process some parameters and collects its output, which it then returns to the client just as if had been fetched from a static file. CGI programs get their input from standard input ( STDIN ) and environment variables. These variables contain information such as the identity of the remote host and user, the value of form elements submitted ( if any ), etc. They also store the server name, the communication protocol, and the name of the software running the server. Once the CGI program starts running, it sends its output back to the web server via standard output ( STDOUT ). The web server takes the output of the CGI script and adds its own HTTP headers before sending it back to the browser of the user who requested it. CGI allows you to generate output that doesn't look any different to the end user than other responses on the Web.
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