book

Mastering Regular Expressions, 3rd Edition

by Jeffrey E.F. Friedl

August 2006

Intermediate to advanced

542 pages

15h 33m

English

O'Reilly Media, Inc.

Read now

Unlock full access

Solving Real ProblemsRegular Expressions as a LanguageThe Filename AnalogyThe Language AnalogyThe Regular-Expression Frame of MindIf You Have Some Regular-Expression ExperienceSearching Text Files: EgrepEgrep MetacharactersStart and End of the LineCharacter ClassesMatching Any Character with DotAlternationIgnoring Differences in CapitalizationWord BoundariesIn a NutshellOptional ItemsOther Quantifiers: RepetitionParentheses and BackreferencesThe Great EscapeExpanding the FoundationLinguistic DiversificationThe Goal of a Regular ExpressionA Few More ExamplesRegular Expression NomenclatureImproving on the Status QuoSummaryPersonal Glimpses
About the ExamplesA Short Introduction to PerlMatching Text with Regular ExpressionsToward a More Real-World ExampleSide Effects of a Successful MatchIntertwined Regular ExpressionsIntermissionModifying Text with Regular ExpressionsExample: Form LetterExample: Prettifying a Stock PriceAutomated EditingA Small Mail UtilityAdding Commas to a Number with LookaroundText-to-HTML ConversionThat Doubled-Word Thing
A Casual Stroll Across the Regex LandscapeThe Origins of Regular ExpressionsAt a GlanceCare and Handling of Regular ExpressionsIntegrated HandlingProcedural and Object-Oriented HandlingA Search-and-Replace ExampleSearch and Replace in Other LanguagesCare and Handling: SummaryStrings, Character Encodings, and ModesStrings as Regular ExpressionsCharacter-Encoding IssuesUnicodeRegex Modes and Match ModesCommon Metacharacters and FeaturesCharacter RepresentationsCharacter Classes and Class-Like ConstructsAnchors and Other “Zero-Width Assertions”Comments and Mode ModifiersGrouping, Capturing, Conditionals, and ControlGuide to the Advanced Chapters
Start Your Engines!Two Kinds of EnginesNew StandardsRegex Engine TypesFrom the Department of Redundancy DepartmentTesting the Engine TypeMatch BasicsAbout the ExamplesRule 1: The Match That Begins Earliest WinsEngine Pieces and PartsRule 2: The Standard Quantifiers Are GreedyRegex-Directed Versus Text-DirectedNFA Engine: Regex-DirectedDFA Engine: Text-DirectedFirst Thoughts: NFA and DFA in ComparisonBacktrackingA Really Crummy AnalogyTwo Important Points on BacktrackingSaved StatesBacktracking and GreedinessMore About Greediness and BacktrackingProblems of GreedinessMulti-Character “Quotes”Using Lazy QuantifiersGreediness and Laziness Always Favor a MatchThe Essence of Greediness, Laziness, and BacktrackingPossessive Quantifiers and Atomic GroupingPossessive Quantifiers, ?+, *+, ++, and {m,n}+The Backtracking of LookaroundIs Alternation Greedy?Taking Advantage of Ordered AlternationNFA, DFA, and POSIX“The Longest-Leftmost”POSIX and the Longest-Leftmost RuleSpeed and EfficiencySummary: NFA and DFA in ComparisonSummary

Regex Balancing ActA Few Short ExamplesContinuing with Continuation LinesMatching an IP AddressWorking with FilenamesMatching Balanced Sets of ParenthesesWatching Out for Unwanted MatchesMatching Delimited TextKnowing Your Data and Making AssumptionsStripping Leading and Trailing WhitespaceHTML-Related ExamplesMatching an HTML TagMatching an HTML LinkExamining an HTTP URLValidating a HostnamePlucking Out a URL in the Real WorldExtended ExamplesKeeping in Sync with Your DataParsing CSV Files
A Sobering ExampleA Simple Change—Placing Your Best Foot ForwardEfficiency Versus CorrectnessAdvancing Further—Localizing the GreedinessReality CheckA Global View of BacktrackingMore Work for a POSIX NFAWork Required During a Non-MatchBeing More SpecificAlternation Can Be ExpensiveBenchmarkingKnow What You’re MeasuringBenchmarking with PHPBenchmarking with JavaBenchmarking with VB.NETBenchmarking with RubyBenchmarking with PythonBenchmarking with TclCommon OptimizationsNo Free LunchEveryone’s Lunch is DifferentThe Mechanics of Regex ApplicationPre-Application OptimizationsOptimizations with the TransmissionOptimizations of the Regex ItselfTechniques for Faster ExpressionsCommon Sense TechniquesExpose Literal TextExpose AnchorsLazy Versus Greedy: Be SpecificSplit Into Multiple Regular ExpressionsMimic Initial-Character DiscriminationUse Atomic Grouping and Possessive QuantifiersLead the Engine to a MatchUnrolling the LoopMethod 1: Building a Regex From Past ExperiencesThe Real “Unrolling-the-Loop” PatternMethod 2: A Top-Down ViewMethod 3: An Internet HostnameObservationsUsing Atomic Grouping and Possessive QuantifiersShort Unrolling ExamplesUnrolling C CommentsThe Freeflowing RegexA Helping Hand to Guide the MatchA Well-Guided Regex is a Fast RegexWrapupIn Summary: Think!
Regular Expressions as a Language ComponentPerl’s Greatest StrengthPerl’s Greatest WeaknessPerl’s Regex FlavorRegex Operands and Regex LiteralsHow Regex Literals Are ParsedRegex ModifiersRegex-Related PerlismsExpression ContextDynamic Scope and Regex Match EffectsSpecial Variables Modified by a MatchThe qr/···/ Operator and Regex ObjectsBuilding and Using Regex ObjectsViewing Regex ObjectsUsing Regex Objects for EfficiencyThe Match OperatorMatch’s Regex OperandSpecifying the Match Target OperandDifferent Uses of the Match OperatorIterative Matching: Scalar Context, with /gThe Match Operator’s Environmental RelationsThe Substitution OperatorThe Replacement OperandThe /e ModifierContext and Return ValueThe Split OperatorBasic SplitReturning Empty ElementsSplit’s Special Regex OperandsSplit’s Match Operand with Capturing ParenthesesFun with Perl EnhancementsUsing a Dynamic Regex to Match Nested PairsUsing the Embedded-Code ConstructUsing local in an Embedded-Code ConstructA Warning About Embedded Code and my VariablesMatching Nested Constructs with Embedded CodeOverloading Regex LiteralsProblems with Regex-Literal OverloadingMimicking Named Capture
“There’s More Than One Way to Do It”Regex Compilation, the /o Modifier, qr/···/, and EfficiencyUnderstanding the “Pre-Match” CopyThe Study FunctionBenchmarkingRegex Debugging InformationFinal Comments
Java’s Regex FlavorJava Support for \p{···} and \P{···}Unicode Line TerminatorsUsing java.util.regexThe Pattern.compile() FactoryPattern’s matcher methodThe Matcher ObjectApplying the RegexQuerying Match ResultsSimple Search and ReplaceAdvanced Search and ReplaceIn-Place Search and ReplaceThe Matcher’s RegionMethod ChainingMethods for Building a ScannerOther Matcher MethodsOther Pattern MethodsPattern’s split Method, with One ArgumentPattern’s split Method, with Two ArgumentsAdditional ExamplesAdding Width and Height Attributes to Image TagsValidating HTML with Multiple Patterns Per MatcherParsing Comma-Separated Values (CSV) TextJava Version DifferencesDifferences Between 1.4.2 and 1.5.0Differences Between 1.5.0 and 1.6
.NET’s Regex FlavorAdditional Comments on the FlavorUsing .NET Regular ExpressionsRegex QuickstartPackage OverviewCore Object OverviewCore Object DetailsCreating Regex ObjectsUsing Regex ObjectsUsing Match ObjectsUsing Group ObjectsStatic “Convenience” FunctionsRegex CachingSupport FunctionsAdvanced .NETRegex AssembliesMatching Nested ConstructsCapture Objects
PHP’s Regex FlavorThe Preg Function Interface“Pattern” ArgumentsThe Preg Functionspreg_matchpreg_match_allpreg_replacepreg_replace_callbackpreg_splitpreg_greppreg_quote“Missing” Preg Functionspreg_regex_to_patternSyntax-Checking an Unknown Pattern ArgumentSyntax-Checking an Unknown RegexRecursive ExpressionsMatching Text with Nested ParenthesesNo Backtracking Into RecursionMatching a Set of Nested ParenthesesPHP Efficiency IssuesThe S Pattern Modifier: “Study”Extended ExamplesCSV Parsing with PHPChecking Tagged Data for Proper Nesting
Chapter 1Chapter 2Chapter 3Chapter 4Chapter 5Chapter 6Chapter 7Chapter 8Chapter 9Chapter 10

Content preview from Mastering Regular Expressions, 3rd Edition

7Perl

Perl has been featured prominently in this book, and with good reason. It is popular, extremely rich with regular expressions, freely and readily obtainable, easily approachable by the beginner, and available for a remarkably wide variety of platforms, including pretty much all flavors of Windows, Unix, and the Mac.

Some of Perl’s programming constructs superficially resemble those of C or other traditional programming languages, but the resemblance stops there. The way you wield Perl to solve a problem—The Perl Way—is different from traditional languages. The overall layout of a Perl program often uses traditional structured and object-oriented concepts, but data processing often relies heavily on regular expressions. In fact, I believe it is safe to say that regular expressions play a key role in virtually all Perl programs. This includes everything from huge 100,000-line systems, right down to simple one-liners, like

% perl -pi -e 's{([-+]?\d+(\.\d*)?)F\b}{sprintf "%.0fC",($1-32)*5/9)eg' *.txt

which goes through *.txt files and replaces Fahrenheit values with Celsius ones (reminiscent of the first example from Chapter 2).

In This Chapter

This chapter looks at everything regex about Perl,^† including details of its regex flavor and the operators that put them to use. This chapter presents the regex-relevant details from the ground up, but I assume that you have at least a basic familiarity with Perl. (If you’ve read Chapter 2, you’re already familiar enough to at least start ...