Beginning Web Development With Perl : From Novice to ... - Nabo

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CHAPTER 5■ ■ ■LWP ModulesLWP is an abbreviation for library of WWW modules in Perl. LWP modules enable you toincorporate common web tasks into your Perl program through a set of functions that canbe imported into your namespace.Using the LWP modules (the LWP, for short), you can perform tasks such as retrievingweb pages, submitting web forms, and mirroring a web site. As with other tasks in Perl, youcould accomplish these same things without the help of the LWP. However, this chapterwill concentrate on using the LWP modules (thus the title). The LWP contains a number ofprotocol methods, including ones to work with HTTP, HTTPS, FTP, NNTP, and others. Thischapter looks at how to use the LWP with HTTP and HTTPS.Getting Started with the LWPTo use the LWP modules, you need to first obtain and install them. Distributions such asDebian have the LWP prepackaged, which makes installation rather trivial (apt-get installlibwww-perl). If your distribution doesn’t contain a prepackaged version of the LWP, you candownload and install the software manually. The LWP modules are available from your favoriteCPAN mirror.It’s always a good idea to check whether the modules are already installed prior to goingthrough the job of installing them. An easy method for testing this is with the following command,executed from the shell:perl -MLWP -e 'print "$LWP::VERSION\n"'5.803You have the LWP installed if you see a version number such as this output:If you don’t have the LWP installed, you’ll need to perform the installation in order toaccomplish most of the tasks in this chapter.The LWP primarily works with the HTTP request and response model. This means thatthe module is an excellent choice for retrieving and parsing web pages on the Internet. Here’sa quick example to get your feet wet. The code (Getua.pl) retrieves a web page and prints it allto STDOUT.89
90CHAPTER 5 ■ LWP MODULESSOLVING A REAL-WORLD PROBLEM WITH THE LWPThe LWP even helped me to get a console gaming system. In 2004, a popular beverage company had a contestthat involved collecting a number of points to earn prizes. These prizes were made available online, butlimited quantities of specific prizes were available. For the more popular items, these quantities were quicklydepleted. In order to ensure that I was one of the lucky people to get the item I wanted—a gaming console—I needed a method to monitor the web page to see when the item became available. Perl to the rescue!Using the LWP I was able to quickly create a script to look for certain text (“Now Available,” for example)to appear on the page, and then send an e-mail alert when the text was found. With this script set to checkevery five minutes, I got the gaming console.Of course, this is just one example of how the LWP can be used to solve a real-world problem, albeita simple one.#!/usr/bin/perl -wuse LWP;use strict;my $browser = LWP::UserAgent->new(agent => 'Perly v1');my $result = $browser->get("http://www.braingia.org/ewfojwefoj");die "An error occurred: ", $result->status_line( ) unless \$result->is_success;#Do something more meaningful with the content than this!print $result->content;When you run this code, it will output the raw web page. It will probably fly past on thescreen, likely ending with something like this:You’ll take a closer look at this code later in the chapter, in the “Retrieving a Web Page”section.HTTP from 29,999 FeetWhile not quite a high-altitude flyover of HTTP—thus 29,999 feet instead of 30,000 feet—thissection gives you a primer on HTTP’s inner workings. RFC 2616 (which can be found athttp://www.rfc-editor.org/) defines the Hypertext Transfer Protocol (HTTP) and providesthe model under which web traffic operates. HTTP is based on requests and responses. InHTTP communications, the requester of a document is the client, and the responder is theserver. When you visit a web page in a browser such as Mozilla Firefox, the browser sends therequest to the server, which then responds accordingly.
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Beginning Web Development with Perl
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PART 5 ■ ■ ■ Creating Web Tem
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■CONTENTSvii■CHAPTER 4 System I
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■CONTENTSixCreating a SOAP Listen
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■CONTENTSxiTemplate Toolkit Synta
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About the Author■STEVE SUEHRING i
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AcknowledgmentsThanks to James Lee
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xx■INTRODUCTIONThis book will use
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CHAPTER 1■ ■ ■The CGI ModuleT
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CHAPTER 1 ■ THE CGI MODULE 5for t
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CHAPTER 1 ■ THE CGI MODULE 33Also
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CHAPTER 2■ ■ ■Popular CGI Mod
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Page 122 and 123: 108CHAPTER 6 ■ NET:: TOOLSCreatin
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Page 126 and 127: 112CHAPTER 6 ■ NET:: TOOLSmy $pop
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142CHAPTER 7 ■ SOAP-BASED WEB SER
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154CHAPTER 8 ■ PERL AND RSSFigure
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156CHAPTER 8 ■ PERL AND RSShttp:/
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158CHAPTER 8 ■ PERL AND RSSDebugg
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160CHAPTER 8 ■ PERL AND RSS$rsswr
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162CHAPTER 8 ■ PERL AND RSSListin
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CHAPTER 9■ ■ ■XML Parsing wit
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CHAPTER 9 ■ XML PARSING WITH PERL
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PART 4■ ■ ■PerformanceEnhance
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184CHAPTER 10 ■ APACHE AND MOD_PE
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202CHAPTER 11 ■ DEVELOPMENT WITH
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CHAPTER 12■ ■ ■The Template T
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CHAPTER 12 ■ THE TEMPLATE TOOLKIT
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CHAPTER 13■ ■ ■Perl Web Sites
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CHAPTER 13 ■ PERL WEB SITES WITH
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284APPENDIX ■ PERL BASICSKeywords
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286APPENDIX ■ PERL BASICS$ perl n
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288APPENDIX ■ PERL BASICSAnd line
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290APPENDIX ■ PERL BASICSCan you
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292APPENDIX ■ PERL BASICSBy defau
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294APPENDIX ■ PERL BASICS#!/usr/b
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296APPENDIX ■ PERL BASICSThe last
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298APPENDIX ■ PERL BASICSThe NOT
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300APPENDIX ■ PERL BASICSprint "S
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304APPENDIX ■ PERL BASICS$ perl s
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306APPENDIX ■ PERL BASICSThis cod
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308APPENDIX ■ PERL BASICS$a = 6 *
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310APPENDIX ■ PERL BASICS$a = "A9
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312APPENDIX ■ PERL BASICS#!/usr/b
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314APPENDIX ■ PERL BASICSmy $name
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316APPENDIX ■ PERL BASICSis short
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320APPENDIX ■ PERL BASICSOther Te
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322APPENDIX ■ PERL BASICS}}}actio
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326APPENDIX ■ PERL BASICSLooping
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330APPENDIX ■ PERL BASICSuntil ($
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332APPENDIX ■ PERL BASICSuse stri
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334APPENDIX ■ PERL BASICSdoneAll
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336APPENDIX ■ PERL BASICS$ perl r
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338APPENDIX ■ PERL BASICSSummaryT
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340■INDEXmethods for retrieving r
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342■INDEXdo() method for, 62dumpi
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344■INDEXhello option for Net::SM
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346■INDEXNet::DNS module, 125-128
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348■INDEXrecord with Net::DNS mod
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350■INDEXstoring mail server in e
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352■INDEXlogging based on, 229pri
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