book

Mastering Perl, 2nd Edition

by brian d foy

January 2014

Intermediate to advanced

400 pages

9h 23m

English

O'Reilly Media, Inc.

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Becoming a MasterWhat It Means to Be a MasterWho Should Read This BookHow to Read This BookWhat Should You Know Already?What I CoverWhat I Don’t CoverStructure of This BookConventions Used in This BookUsing Code ExamplesSafari® Books OnlineHow to Contact UsAcknowledgments
Readable Regexes, /x and (?#…)Global MatchingGlobal Match AnchorsRecursive Regular ExpressionsRepeating a SubpatternLookaroundsLookahead Assertions, (?=PATTERN) and (?!PATTERN)Positive lookahead assertionsNegative lookahead assertionsLookbehind Assertions, (?<!PATTERN) and (?<=PATTERN)Debugging Regular ExpressionsThe -D SwitchSummaryFurther Reading
Bad Data Can Ruin Your DayTaint CheckingWarnings Instead of Fatal ErrorsAutomatic Taint Modemod_perlTainted DataSide Effects of Taint CheckingUntainting DataIO::Handle::untaintHash KeysTaint::UtilChoosing Untainted Data with Tainted DataSymbolic ReferencesDefensive Database Programming with DBIList Forms of system and execThree-Argument opensysopenLimit Special PrivilegesSafe CompartmentsSafe LimitationsA Little FunSummaryFurther Reading
Before You Waste Too Much TimeThe Best Debugger in the WorldSafely Changing ModulesWrapping SubroutinesThe Perl DebuggerAlternative DebuggersUsing a Different Debugger with -dDevel::ptkdbDevel::ebugDevel::hdbIDE DebuggersEPICKomodoSummaryFurther Reading
Finding the CulpritThe General ApproachProfiling DBIOther DBI::Profile ReportsMaking It Even EasierSwitching DatabasesDevel::NYTProfWriting My Own ProfilerDevel::LineCounterProfiling Test SuitesDevel::CoverSummaryFurther Reading
Benchmarking TheoryBenchmarking TimeComparing CodeDon’t Turn Off Your Thinking CapIsolating the EnvironmentHandling OutliersMemory UseThe perlbench ToolSummaryFurther Reading
Good StyleperltidyDeobfuscationDe-encoding Hidden SourceUnparsing Code with B::DeparsePerl::CriticCreating My Own Perl::Critic PolicySummaryFurther Reading
Package and Lexical VariablesGetting the Package VersionThe Symbol TableTypeglobsAliasingFilehandle Arguments in Older CodeNaming Anonymous SubroutinesThe Easy WaySummaryFurther Reading
Subroutines as DataCreating and Replacing Named SubroutinesSymbolic ReferencesIterating Through Subroutine ListsProcessing PipelinesSelf-Referencing Anonymous SubroutinesMethod ListsSubroutines as ArgumentsAutoloaded MethodsHashes as ObjectsAutoSplitSummaryFurther Reading
Choosing the Right SolutionSending Patches to the AuthorLocal PatchesTaking Over a ModuleForkingStarting Over on My OwnReplacing Module PartsSubclassingAn ExtUtils::MakeMaker ExampleOther ExamplesWrapping SubroutinesSummaryFurther Reading

Things Not to DoCode in a Separate FileBetter WaysEnvironment VariablesSpecial Environment VariablesTurning on Extra OutputCommand-Line SwitchesThe -s SwitchGetopt ModulesGetopt::StdGetopt::LongConfiguration FilesConfigReader::SimpleConfig::IniFilesConfig::ScopedOther Configuration FormatsScripts with a Different NameInteractive and Noninteractive Programsperl’s ConfigDifferent Operating SystemsSummaryFurther Reading
Perl Error BasicsOperating System ErrorsChild Process ErrorsErrors Specific to the Operating SystemReporting Module ErrorsSeparation of ConcernsExceptionsevalMultiple Levels of diedie with a ReferencePropagating Objects with dieClobbering $@autodieReporting the CulpritCatching ExceptionsTry::TinyTryCatchPolymorphic Return ValuesSummaryFurther Reading
Recording Errors and Other InformationLog4perlSubroutine ArgumentsConfiguring Log4perlAdding my own informationPersistent ConfigurationLogging CategoriesCategories are hierarchicalOther Log::Log4perl FeaturesSummaryFurther Reading
Perl-Specific FormatspackFixed-Length RecordsUnpacking Binary FormatsData::DumperSimilar ModulesStorableFreezing DataStorable’s Security ProblemSerealDBM FilesdbmopenDBM::DeepPerl-Agnostic FormatsJSONYAMLYAML module variantsMessagePackSummaryFurther Reading
The Pod FormatDirectivesEncodingBody ElementsTranslating PodPod TranslatorsPod::Perldoc::ToTocPod::SimpleSubclassing Pod::SimplePod in Your Web ServerTesting PodChecking PodPod CoverageHiding and Ignoring FunctionsSummaryFurther Reading
Binary NumbersWriting in BinaryBit OperatorsUnary NOT (~)Bitwise AND (&)Binary OR (|)Exclusive OR (^)Left << and Right >> Shift OperatorsBit VectorsThe vec FunctionBit String StorageStoring DNAChecking PrimesKeeping Track of ThingsSummaryFurther Reading
They Look Like Normal VariablesAt the User LevelBehind the CurtainScalarsTie::CycleBounded IntegersSelf-Destructing ValuesArraysReinventing ArraysSomething a Bit More RealisticHashesFilehandlesSummaryFurther Reading
The main ThingBacking UpWho’s Calling?Testing the ProgramModules as TestsCreating a Program DistributionAdding to the ScriptDistributing the ProgramsSummaryFurther Reading
Perl BooksNon-Perl Books
My Philosophy of Problem-SolvingMy MethodSome Stupid Things I’ve Done and Still Do

Content preview from Mastering Perl, 2nd Edition

Chapter 3. Perl Debuggers

The standard Perl distribution comes with a debugger, although it’s really just another Perl program, perl5db.pl. Since it is just a program, I can use it as the basis for writing my own debuggers to suit my needs, or I can use the interface perl5db.pl provides to configure its actions. That’s just the beginning, though. I can write my own debugger or use one of the many debuggers created by other Perl masters.

This chapter isn’t about actually debugging Perl source code to find problems; people have written entire books about that. The more you practice Perl, the better you should get at that.

Before You Waste Too Much Time

Before I get started, I’m almost required to remind you that Perl offers two huge debugging aids: strict and warnings. I have the most trouble with smaller programs where I don’t think I need strict and I make the stupid mistakes it would have caught. I spend much more time than I should tracking down something Perl would have shown me instantly. It’s the common mistakes that seem to be the hardest for me to debug. Learn from the master: don’t discount strict or warnings for even small programs.

Now that I’ve said that, you’re going to look for it in the examples in this chapter. Just pretend those lines are there, and the book costs a bit less for the extra half a page that I saved by omitting those lines. Or, if you don’t like that, just imagine that I’m running every program with both strict and warnings turned on from the command line: ...