B.16. The Common Gateway Interface (CGI)
One of the most popular uses for Perl on the Web is in writing CGI programs. These run on a web server to process the results of a form, perform a search, produce dynamic web content, or count the number of accesses to a web page.
The CGI module, which comes with Perl, provides an easy way to access the form parameters and to generate some HTML in responses. (If you don't want the overhead of the full CGI module, the CGI_Lite module provides access to the form parameters without all the rest.) It may be tempting to skip the module and simply copy-and-paste one of the snippets of code that purport to give access to the form parameters, but nearly all of these are buggy.
When writing CGI programs, though, there are several big issues to keep in mind. These make this topic one too broad to fully include in this book:
And that list didn't even mention URI-encoding, HTML entities, HTTP and response codes, Secure Sockets Layer (SSL), Server-side Includes (SSI), here documents, creating graphics on the fly, programmatically generating HTML tables, forms, and widgets, hidden form elements, getting and setting cookies, path info, error trapping, redirection, taint checking, internationalization and localization, embedding Perl into HTML (or the other way around), working with Apache and mod_perl, and using the LWP module. Most or all of those topics should be covered in any good book on using Perl with the Web. CGI Programming with Perl by Scott Guelich, et al. (O'Reilly & Associates, Inc.) is mighty nice here, as is Lincoln Stein's Network Programming with Perl (Addison-Wesley).
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