chapter 1: introduction- web client programming with perl

một miễn phí từ oreilly xuất bản, web client lập trình với perl, một phiên bản trực tuyến. cuốn sách này là cho các quản trị web những người duy trì một lượng lớn dữ liệu. quản trị viên có thể thay thế nhiệm vụ bảo trì hướng dẫn sử dụng với các robot web để phát hiện và sửa các vấn đề với các trang web. robot thực hiện nhiệm vụ chính xác hơn và nhanh chóng hơn so với bàn tay con người....
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chapter 1:introduction- web client programming with perl Chapter 1:Introduction- Web Client Programming with PerlSo what does Web client programming mean, and what do you need to learnto do it?A web client is an application that communicates with a web server, usingHypertext Transfer Protocol (HTTP). Hypertext Transfer Protocol is theprotocol behind the World Wide Web. With every web transaction, HTTP isinvoked. HTTP is behind every request for a web document or graphic,every click of a hypertext link, and every submission of a form. The Web isabout distributing information over the Internet, and HTTP is the protocolused to do so.Most web users never think about HTTP, just as most TV viewers dontthink about how video images get from the studio to their home. But thisbook is not for the average web user. This book is for people who want to dosomething that available web software wont let them do.Why Write Your Own Clients?With the proliferation of available web browsers, you might wonder whyyou would want to write your own client program. The answer is that bywriting your own client programs, you can leap beyond the preprogrammedfunctionality of a browser. For example, the following scenarios are allpossible:  An urgent document is sent out via Federal Express, and the sender wants to know the status of the document the moment it becomes available. He enters the FedEx airbill tracking number into a program that notifies him of events as the FedEx server reports them. Since the document is urgent, he configures the program to contact him if the document is not delivered by the next morning. A system administrator would like to verify that all hyperlinks and image references are valid at her site. She runs a program to verify all documents at the site and report the results. She then finds some common mistakes in numerous documents, and runs another program to automatically fix them. An investor keeps a stock portfolio online and runs a program to check stock prices. The online portfolio is updated automatically as prices change, and the program can notify the investor when there is an unusual jump in a stock price. A college student connects his computer to the Internet via an Ethernet connection in his room. The university distributes custom software that will allow his computer to wake him up every morning with local news. Audio clips are downloaded and a web browser is launched. As the sound clips play, the browser automatically updates to display a new image that corresponds to the report. A weather map is displayed when the local weather is being announced. Images of the campus are displayed as local news is announced. National and international news briefs are presented in this automatic fashion, and the program can be configured to omit and include certain topics. The student may flunk biology, but at least hell be the first to know who won the Bulls game.And so on. Think about resources that you regularly visit on the Web.Maybe every morning you check the David Letterman top ten list from lastnight, and before you leave the office you check the weather report. Can youautomate those visits? Think about that time you wanted to print an entiredocument that had been split up into individual files, and had to selectChapter 1, print, return to the contents page, select Chapter 2, etc. Is there away to print the entire thing in one swoop?Browsers are for browsing. They are wonderful tools for discovery, fortraveling to far-off virtual lands. But once you know what you want, a morespecialized client might be more effective for your needs.The Web and HTTPIf you dont know what the Web is, you probably picked up the wrong book.But heres some history and background, just to make sure were all comingfrom the same place.The World Wide Web was developed in 1990 by Tim Berners-Lee at theConseil Europeen pour la Recherche Nucleaire (CERN). The inspirationbehind it was simply to find a way to share results of experiments in high-energy particle physics. The central technology behind the Web was theability to link from a document on one server to a document on another,keeping the actual location and access method of the documents invisible tothe user. Certainly not the sort of thing that youd expect to start a mediacircus.So what did start the media circus? In 1993 a graphical interface to the Web,named Mosaic, was developed at the University of Illinois at Urbana-Champaign. At first, Mosaic ran only on UNIX systems running the XWindow System, a platform that was popular with academics but unknownto practically anyone else. Yet anyone who saw Mosaic in action knewimmediately that this was big news. Soon afterwards, Mac and PC versionscame out, and the Web started to become immensely ...