131 lines
8.4 KiB
HTML
131 lines
8.4 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta name="Robots" content="index,follow" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="topic" />
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<meta name="DC.Title" content="Overview of CGI" />
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<meta name="abstract" content="This topic provides information about CGI. Common Gateway Interface (CGI) is a standard, supported by almost all web servers, that defines how information is exchanged between a web server and an external program (CGI program)." />
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<meta name="description" content="This topic provides information about CGI. Common Gateway Interface (CGI) is a standard, supported by almost all web servers, that defines how information is exchanged between a web server and an external program (CGI program)." />
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<meta name="DC.Relation" scheme="URI" content="rzaieparcgi.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2002,2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2002,2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rzag3ch1overview" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Overview of CGI</title>
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</head>
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<body id="rzag3ch1overview"><a name="rzag3ch1overview"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Overview of CGI</h1>
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<div><p>This topic provides information about CGI. Common Gateway Interface
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(CGI) is a standard, supported by almost all web servers, that defines how
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information is exchanged between a web server and an external program (CGI
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program). </p>
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<p>The CGI specification dictates how CGI programs get their input and how
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they produce any output. CGI programs process data that is received from browser
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clients. For example, the client fills out a form and sends the information
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back to the server. Then the server runs the CGI program. </p>
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<p>Programs that are called by the server must conform to the server CGI interface
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in order to run properly. We will describe this in further detail later in
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this chapter. </p>
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<p>The administrator controls which CGI programs the system can run by using
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the server directives. The server recognizes a URL that contains a request
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for a CGI program, commonly called a CGI script. Depending on the server directives,
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the server calls that program on behalf of the client browser. </p>
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<p>The server supports CGI programs that are written in C++, REXX, ILE C,
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ILE RPG, and ILE COBOL. It also supports multi-thread CGI programs in all
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of these languages capable of multiple threads.</p>
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<p>You need to compile programs that are written in programming languages.
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Compiled programs typically run faster than programs that are written in scripting
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languages. On the other hand, those programs that are written in scripting
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languages tend to be easier to write, maintain, and debug.</p>
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<p>The functions and tasks that CGI programs can perform range from the simple
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to the very advanced. In general, we call those that perform the simple tasks
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CGI scripts because you do not compile them. We often call those that perform
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complex tasks gateway programs. In this manual, we refer to both types as <dfn class="term">CGI
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programs</dfn>.</p>
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<p>Given the wide choice of languages and the variety of functions, the possible
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uses for CGI programs seem almost endless. How you use them is up to you.
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Once you understand the CGI specification, you will know how servers pass
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input to CGI programs and how servers expect output.</p>
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<p>There are many uses for CGI programs. Basically, you should design them
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to handle dynamic information. Dynamic in this context refers to temporary
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information that is created for a one-time use and not stored as a static
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Web page. This information may be a document, an e-mail message, or the results
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of a conversion program.</p>
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<p>For detailed information about CGI APIs, see Chapter 8, “HTTP
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Server Application Programming Interfaces” on page 51.</p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaieparcgi.htm" title="This topic provides information about Common Gateway Interfaces (CGI).">Common Gateway Interface</a></div>
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</div>
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</div><div class="nested1" xml:lang="en-us" id="cgianddynamicdocuments"><a name="cgianddynamicdocuments"><!-- --></a><h2 class="topictitle2">CGI and Dynamic Documents</h2>
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<div><p>There are many types of files that exist on the web. Primarily they fall
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into one of the following categories:</p>
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<ul><li>Images</li>
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<li>Multimedia</li>
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<li>Programs</li>
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<li>HTML documents</li>
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</ul>
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<p>Servers break HTML documents into two distinct types:</p>
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<ul><li>Static</li>
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<li>Dynamic</li>
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</ul>
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<p><dfn class="term">Static documents</dfn> exist in non-changing source form on the
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web server. You should create <dfn class="term">Dynamic documents</dfn> as temporary
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documents to satisfy a specific, individual request.</p>
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<p>Consider the process of ″serving″ these two types of documents. Responding
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to requests for static documents is fairly simple. For example, Jill User
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accesses the Acme web server to get information on the Pro-Expert gas grill.
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She clicks on Products, then on Grills, and finally on Pro-Expert. Each time
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Jill clicks on a link, the web browser uses the URL that is attached to the
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link to request a specific document from the web server. The server responds
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by sending a copy of the document to Jill’s browser.</p>
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<p>What if Jill decides that, she wants to search through the information
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on the Acme web server for all documents that contain information on Acme
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grills? Such information could consist of news articles, press releases, price
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listings, and service agreements. This is a more difficult request to process.
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This is not a request for an existing document. Instead, it is a request for
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a dynamically generated list of documents that meet certain criteria. This
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is where CGI comes in.</p>
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<p>You can use a CGI program to parse the request and search through the documents
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on your web server. You can also use it to create a list with hypertext links
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to each of the documents that contain the specified word or string.</p>
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</div>
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</div>
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<div class="nested1" xml:lang="en-us" id="usesforcgi"><a name="usesforcgi"><!-- --></a><h2 class="topictitle2">Uses for CGI</h2>
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<div><p>HTML allows you to access resources on the Internet by using other protocols
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that are specified in the URL. Examples of such protocols are <samp class="codeph">mailto</samp>, <samp class="codeph">ftp</samp>,
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and <samp class="codeph">news</samp>. If you code a link with <samp class="codeph">mailto</samp> that
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is followed by an e-mail address, the link will result in a generic mail form.</p>
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<p>What if you wanted your customers to provide specific information, such
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as how often they use the web? Or how they heard about your company? Rather
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than using the generic <samp class="codeph">mailto</samp> form, you can create a form
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that asks these questions and more. You can then use a CGI program to interpret
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the information, include it in an e-mail message, and send it to the appropriate
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person.</p>
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<p>You do not need to limit CGI programs to processing search requests and
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e-mail. You can use them for a wide variety of purposes. Basically, anytime
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you want to take input from the reader and generate a response, you can use
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a CGI program. The input may even be apparent to the reader. For example,
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many people want to know how many other people have visited their home page.
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You can create a CGI program that keeps track of the number of requests for
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your home page. This program can display the new total each time someone links
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to your home page.</p>
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</div>
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</div>
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</body>
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</html>
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