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

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CHAPTER 2■ ■ ■Popular CGI ModulesAlong with the CGI module, introduced in Chapter 1, a number of other modules and helperapplications can make your Perl application quite powerful. This chapter examines some ofthose modules and helper applications. It also provides an example of coding program behaviorbased on environment variables, another concept introduced in Chapter 1. Finally, you’lllook at the security considerations related to using the modules discussed in this chapter.Integration with Other ModulesThe CGI module is central to development of CGI applications in Perl. However, the CGImodule is not the only module useful to the Perl CGI programmer. This section examinesa couple of the popular modules used with CGI programs developed in Perl, includingCGI::Carp, URI::Escape, Net::SMTP, mod_perl, and HTML::Mason.■Note Like the previous chapter (and subsequent chapters) of the book, this chapter assumes that you arefamiliar with Perl programming basics. If you’re unfamiliar with Perl, refer to this book’s appendix.CGI::CarpThe Carp module, introduced in Chapter 1, assists in the handling of error messages by providingmore useful information. The CGI::Carp module is the CGI version of that module.Using CGI::Carp, you can send errors to a custom log file rather than to the default webserver log. You can also send errors directly to the browser in place of the dreaded InternalServer Error message.You call the CGI::Carp module with a use statement, just as you invoke as any other module:use CGI::Carp;By default, many useful methods are exported by this simple invocation. However, somemethods are not exported by default. Some of these will be highlighted in upcoming sections.Table 2-1 shows the Carp functions for outputting warnings and errors. By default, theseare sent to STDERR, which is usually written to the web server error log. As you’ll see next, youcan change the destination for Carp-generated errors.35
36CHAPTER 2 ■ POPULAR CGI MODULESTable 2-1. Carp Functions for Outputting Warnings and ErrorsFunctioncarp()cluck()confess()croak()DescriptionSends a warning of errors. It is not fatal.Sends a warning of errors, including a stack backtrace. It is not fatal.Sends a fatal error, including a stack backtrace.Sends a fatal error.Sending Fatal Errors to the BrowserWith CGI::Carp, you can configure errors to be sent to the browser window rather than tothe log file. This might be useful for debugging and other purposes. However, you shouldbe aware of the potential for this method to divulge too much information to the end user.In other words, using this method makes debugging and testing easier, but it also may giveout too much information about the script, including its location and other items that youmight not wish disclosed. Therefore, if you’re going to use this method, it’s a good idea todisable it before going live with the application.To send errors to the browser, you need to use one of the methods that is not exported bydefault; therefore, you must call it explicitly. Listing 2-1 provides an example of using CGI:Carpto send fatal error messages to the browser.Listing 2-1. Sending an Error to the Browser with CGI::Carp#!/usr/bin/perl -Tuse strict;use CGI qw/:standard/;use CGI::Carp qw/fatalsToBrowser/;print header,start_html("Testing CGI Carp");die ("This is a test die");print end_html;exit;Viewing the code in a browser reveals a page like the one in Figure 2-1.CGI::Carp takes care of most of the background work for you once you call the correctmethod, with this line of code:use CGI::Carp qw(fatalsToBrowser);From there, if the script dies, the error will be sent to the browser.As you can see in Figure 2-1, the error message also shows contact information. You canconfigure this message by calling the set_message() function. Like the fatalsToBrowser()function, set_message() needs to be explicitly imported into your namespace:use CGI::Carp qw(fatalsToBrowser set_message);
Page 3 and 4: Beginning Web Development with Perl
Page 5 and 6: PART 5 ■ ■ ■ Creating Web Tem
Page 8 and 9: ■CONTENTSvii■CHAPTER 4 System I
Page 10 and 11: ■CONTENTSixCreating a SOAP Listen
Page 12 and 13: ■CONTENTSxiTemplate Toolkit Synta
Page 14 and 15: About the Author■STEVE SUEHRING i
Page 16 and 17: AcknowledgmentsThanks to James Lee
Page 18 and 19: xx■INTRODUCTIONThis book will use
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86CHAPTER 4 ■ SYSTEM INTERACTIONr
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CHAPTER 5■ ■ ■LWP ModulesLWP
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CHAPTER 5 ■ LWP MODULES 91HTTP Re
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CHAPTER 5 ■ LWP MODULES 93Get Fun
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108CHAPTER 6 ■ NET:: TOOLSCreatin
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110CHAPTER 6 ■ NET:: TOOLSThe out
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112CHAPTER 6 ■ NET:: TOOLSmy $pop
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114CHAPTER 6 ■ NET:: TOOLSthe POP
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116CHAPTER 6 ■ NET:: TOOLS($messa
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118CHAPTER 6 ■ NET:: TOOLSListing
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120CHAPTER 6 ■ NET:: TOOLSFor the
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122CHAPTER 6 ■ NET:: TOOLSNet::SM
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124CHAPTER 6 ■ NET:: TOOLS$smtpco
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126CHAPTER 6 ■ NET:: TOOLSuse Net
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128CHAPTER 6 ■ NET:: TOOLSListing
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130CHAPTER 6 ■ NET:: TOOLSFor exa
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132CHAPTER 6 ■ NET:: TOOLSSending
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PART 3■ ■ ■XML and RSS
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138CHAPTER 7 ■ SOAP-BASED WEB SER
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154CHAPTER 8 ■ PERL AND RSSFigure
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156CHAPTER 8 ■ PERL AND RSShttp:/
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158CHAPTER 8 ■ PERL AND RSSDebugg
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160CHAPTER 8 ■ PERL AND RSS$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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294APPENDIX ■ PERL BASICS#!/usr/b
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296APPENDIX ■ PERL BASICSThe last
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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 $name
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316APPENDIX ■ PERL BASICSis short
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334APPENDIX ■ PERL BASICSdoneAll
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336APPENDIX ■ PERL BASICS$ 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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