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.

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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

10PHP

PHP’s popularity exploded during the early phases of the late-90s web boom and remains wildly popular today. One reason for this popularity is that even non-engineers can start using its basic features with very little preparation. Yet, despite this approachability, PHP also provides a vast cornucopia of advanced features and functions sure to please the seasoned engineer. PHP supports regular expressions, of course, and does so with no less than three separate, unrelated regex engines.

The three regex engines in PHP are the “preg,” “ereg,” and “mb_ereg” engines. This book covers the preg suite of functions. It’s backed by an NFA engine that is generally superior, in both features and speed, to the other two. (“preg” is normally pronounced “p-reg.”)

Reliance on Early Chapters Before looking at what’s in this chapter, it’s important to emphasize that it relies heavily on the base material in Chapters 1 through 6. Readers interested only in PHP may be inclined to start their reading with this chapter, but I want to encourage them not to miss the benefits of the preface (in particular, the typographical conventions) and the earlier chapters: Chapters 1, 2, and 3 introduce basic concepts, features, and techniques involved with regular expressions, while Chapters 4, 5, and 6 offer important keys to regex understanding that directly apply to PHP’s preg engine. Among the important concepts covered in earlier chapters are the base mechanics of how an NFA regex engine goes about ...