- •Introduction
- •Who This Book Is For
- •What This Book Covers
- •How This Book Is Structured
- •What You Need to Use This Book
- •Conventions
- •Source Code
- •Errata
- •p2p.wrox.com
- •What Are Regular Expressions?
- •What Can Regular Expressions Be Used For?
- •Finding Doubled Words
- •Checking Input from Web Forms
- •Changing Date Formats
- •Finding Incorrect Case
- •Adding Links to URLs
- •Regular Expressions You Already Use
- •Search and Replace in Word Processors
- •Directory Listings
- •Online Searching
- •Why Regular Expressions Seem Intimidating
- •Compact, Cryptic Syntax
- •Whitespace Can Significantly Alter the Meaning
- •No Standards Body
- •Differences between Implementations
- •Characters Change Meaning in Different Contexts
- •Regular Expressions Can Be Case Sensitive
- •Case-Sensitive and Case-Insensitive Matching
- •Case and Metacharacters
- •Continual Evolution in Techniques Supported
- •Multiple Solutions for a Single Problem
- •What You Want to Do with a Regular Expression
- •Replacing Text in Quantity
- •Regular Expression Tools
- •findstr
- •Microsoft Word
- •StarOffice Writer/OpenOffice.org Writer
- •Komodo Rx Package
- •PowerGrep
- •Microsoft Excel
- •JavaScript and JScript
- •VBScript
- •Visual Basic.NET
- •Java
- •Perl
- •MySQL
- •SQL Server 2000
- •W3C XML Schema
- •An Analytical Approach to Using Regular Expressions
- •Express and Document What You Want to Do in English
- •Consider the Regular Expression Options Available
- •Consider Sensitivity and Specificity
- •Create Appropriate Regular Expressions
- •Document All but Simple Regular Expressions
- •Document What You Expect the Regular Expression to Do
- •Document What You Want to Match
- •Test the Results of a Regular Expression
- •Matching Single Characters
- •Matching Sequences of Characters That Each Occur Once
- •Introducing Metacharacters
- •Matching Sequences of Different Characters
- •Matching Optional Characters
- •Matching Multiple Optional Characters
- •Other Cardinality Operators
- •The * Quantifier
- •The + Quantifier
- •The Curly-Brace Syntax
- •The {n} Syntax
- •The {n,m} Syntax
- •Exercises
- •Regular Expression Metacharacters
- •Thinking about Characters and Positions
- •The Period (.) Metacharacter
- •Matching Variably Structured Part Numbers
- •Matching a Literal Period
- •The \w Metacharacter
- •The \W Metacharacter
- •Digits and Nondigits
- •The \d Metacharacter
- •Canadian Postal Code Example
- •The \D Metacharacter
- •Alternatives to \d and \D
- •The \s Metacharacter
- •Handling Optional Whitespace
- •The \S Metacharacter
- •The \t Metacharacter
- •The \n Metacharacter
- •Escaped Characters
- •Finding the Backslash
- •Modifiers
- •Global Search
- •Case-Insensitive Search
- •Exercises
- •Introduction to Character Classes
- •Choice between Two Characters
- •Using Quantifiers with Character Classes
- •Using the \b Metacharacter in Character Classes
- •Selecting Literal Square Brackets
- •Using Ranges in Character Classes
- •Alphabetic Ranges
- •Use [A-z] With Care
- •Digit Ranges in Character Classes
- •Hexadecimal Numbers
- •IP Addresses
- •Reverse Ranges in Character Classes
- •A Potential Range Trap
- •Finding HTML Heading Elements
- •Metacharacter Meaning within Character Classes
- •The ^ metacharacter
- •How to Use the - Metacharacter
- •Negated Character Classes
- •Combining Positive and Negative Character Classes
- •POSIX Character Classes
- •The [:alnum:] Character Class
- •Exercises
- •String, Line, and Word Boundaries
- •The ^ Metacharacter
- •The ^ Metacharacter and Multiline Mode
- •The $ Metacharacter
- •The $ Metacharacter in Multiline Mode
- •Using the ^ and $ Metacharacters Together
- •Matching Blank Lines
- •Working with Dollar Amounts
- •Revisiting the IP Address Example
- •What Is a Word?
- •Identifying Word Boundaries
- •The \< Syntax
- •The \>Syntax
- •The \b Syntax
- •The \B Metacharacter
- •Less-Common Word-Boundary Metacharacters
- •Exercises
- •Grouping Using Parentheses
- •Parentheses and Quantifiers
- •Matching Literal Parentheses
- •U.S. Telephone Number Example
- •Alternation
- •Choosing among Multiple Options
- •Unexpected Alternation Behavior
- •Capturing Parentheses
- •Numbering of Captured Groups
- •Numbering When Using Nested Parentheses
- •Named Groups
- •Non-Capturing Parentheses
- •Back References
- •Exercises
- •Why You Need Lookahead and Lookbehind
- •The (? metacharacters
- •Lookahead
- •Positive Lookahead
- •Negative Lookahead
- •Positive Lookahead Examples
- •Positive Lookahead in the Same Document
- •Inserting an Apostrophe
- •Lookbehind
- •Positive Lookbehind
- •Negative Lookbehind
- •How to Match Positions
- •Adding Commas to Large Numbers
- •Exercises
- •What Are Sensitivity and Specificity?
- •Extreme Sensitivity, Awful Specificity
- •Email Addresses Example
- •Replacing Hyphens Example
- •The Sensitivity/Specificity Trade-Off
- •Sensitivity, Specificity, and Positional Characters
- •Sensitivity, Specificity, and Modes
- •Sensitivity, Specificity, and Lookahead and Lookbehind
- •How Much Should the Regular Expressions Do?
- •Abbreviations
- •Characters from Other Languages
- •Names
- •Sensitivity and How to Achieve It
- •Specificity and How to Maximize It
- •Exercises
- •Documenting Regular Expressions
- •Document the Problem Definition
- •Add Comments to Your Code
- •Making Use of Extended Mode
- •Know Your Data
- •Abbreviations
- •Proper Names
- •Incorrect Spelling
- •Creating Test Cases
- •Debugging Regular Expressions
- •Treacherous Whitespace
- •Backslashes Causing Problems
- •Considering Other Causes
- •The User Interface
- •Metacharacters Available
- •Quantifiers
- •The @ Quantifier
- •The {n,m} Syntax
- •Modes
- •Character Classes
- •Back References
- •Lookahead and Lookbehind
- •Lazy Matching versus Greedy Matching
- •Examples
- •Character Class Examples, Including Ranges
- •Whole Word Searches
- •Search-and-Replace Examples
- •Changing Name Structure Using Back References
- •Manipulating Dates
- •The Star Training Company Example
- •Regular Expressions in Visual Basic for Applications
- •Exercises
- •The User Interface
- •Metacharacters Available
- •Quantifiers
- •Modes
- •Character Classes
- •Alternation
- •Back References
- •Lookahead and Lookbehind
- •Search Example
- •Search-and-Replace Example
- •Online Chats
- •POSIX Character Classes
- •Matching Numeric Digits
- •Exercises
- •Introducing findstr
- •Finding Literal Text
- •Quantifiers
- •Character Classes
- •Command-Line Switch Examples
- •The /v Switch
- •The /a Switch
- •Single File Examples
- •Simple Character Class Example
- •Find Protocols Example
- •Multiple File Example
- •A Filelist Example
- •Exercises
- •The PowerGREP Interface
- •A Simple Find Example
- •The Replace Tab
- •The File Finder Tab
- •Syntax Coloring
- •Other Tabs
- •Numeric Digits and Alphabetic Characters
- •Quantifiers
- •Back References
- •Alternation
- •Line Position Metacharacters
- •Word-Boundary Metacharacters
- •Lookahead and Lookbehind
- •Longer Examples
- •Finding HTML Horizontal Rule Elements
- •Matching Time Example
- •Exercises
- •The Excel Find Interface
- •Escaping Wildcard Characters
- •Using Wildcards in Data Forms
- •Using Wildcards in Filters
- •Exercises
- •Using LIKE with Regular Expressions
- •The % Metacharacter
- •The _ Metacharacter
- •Character Classes
- •Negated Character Classes
- •Using Full-Text Search
- •Using The CONTAINS Predicate
- •Document Filters on Image Columns
- •Exercises
- •Using the _ and % Metacharacters
- •Testing Matching of Literals: _ and % Metacharacters
- •Using Positional Metacharacters
- •Using Character Classes
- •Quantifiers
- •Social Security Number Example
- •Exercises
- •The Interface to Metacharacters in Microsoft Access
- •Creating a Hard-Wired Query
- •Creating a Parameter Query
- •Using the ? Metacharacter
- •Using the * Metacharacter
- •Using the # Metacharacter
- •Using the # Character with Date/Time Data
- •Using Character Classes in Access
- •Exercises
- •The RegExp Object
- •Attributes of the RegExp Object
- •The Other Properties of the RegExp Object
- •The test() Method of the RegExp Object
- •The exec() Method of the RegExp Object
- •The String Object
- •Metacharacters in JavaScript and JScript
- •SSN Validation Example
- •Exercises
- •The RegExp Object and How to Use It
- •Quantifiers
- •Positional Metacharacters
- •Character Classes
- •Word Boundaries
- •Lookahead
- •Grouping and Nongrouping Parentheses
- •Exercises
- •The System.Text.RegularExpressions namespace
- •A Simple Visual Basic .NET Example
- •The Classes of System.Text.RegularExpressions
- •The Regex Object
- •Using the Match Object and Matches Collection
- •Using the Match.Success Property and Match.NextMatch Method
- •The GroupCollection and Group Classes
- •The CaptureCollection and Capture Class
- •The RegexOptions Enumeration
- •Case-Insensitive Matching: The IgnoreCase Option
- •Multiline Matching: The Effect on the ^ and $ Metacharacters
- •Right to Left Matching: The RightToLeft Option
- •Lookahead and Lookbehind
- •Exercises
- •An Introductory Example
- •The Classes of System.Text.RegularExpressions
- •The Regex Class
- •The Options Property of the Regex Class
- •Regex Class Methods
- •The CompileToAssembly() Method
- •The GetGroupNames() Method
- •The GetGroupNumbers() Method
- •GroupNumberFromName() and GroupNameFromNumber() Methods
- •The IsMatch() Method
- •The Match() Method
- •The Matches() Method
- •The Replace() Method
- •The Split() Method
- •Using the Static Methods of the Regex Class
- •The IsMatch() Method as a Static
- •The Match() Method as a Static
- •The Matches() Method as a Static
- •The Replace() Method as a Static
- •The Split() Method as a Static
- •The Match and Matches Classes
- •The Match Class
- •The GroupCollection and Group Classes
- •The RegexOptions Class
- •The IgnorePatternWhitespace Option
- •Metacharacters Supported in Visual C# .NET
- •Using Named Groups
- •Using Back References
- •Exercise
- •The ereg() Set of Functions
- •The ereg() Function
- •The ereg() Function with Three Arguments
- •The eregi() Function
- •The ereg_replace() Function
- •The eregi_replace() Function
- •The split() Function
- •The spliti() Function
- •The sql_regcase() Function
- •Perl Compatible Regular Expressions
- •Pattern Delimiters in PCRE
- •Escaping Pattern Delimiters
- •Matching Modifiers in PCRE
- •Using the preg_match() Function
- •Using the preg_match_all() Function
- •Using the preg_grep() Function
- •Using the preg_quote() Function
- •Using the preg_replace() Function
- •Using the preg_replace_callback() Function
- •Using the preg_split() Function
- •Supported Metacharacters with ereg()
- •Using POSIX Character Classes with PHP
- •Supported Metacharacters with PCRE
- •Positional Metacharacters
- •Character Classes in PHP
- •Documenting PHP Regular Expressions
- •Exercises
- •W3C XML Schema Basics
- •Tools for Using W3C XML Schema
- •Comparing XML Schema and DTDs
- •How Constraints Are Expressed in W3C XML Schema
- •W3C XML Schema Datatypes
- •Derivation by Restriction
- •Unicode and W3C XML Schema
- •Unicode Overview
- •Using Unicode Character Classes
- •Matching Decimal Numbers
- •Mixing Unicode Character Classes with Other Metacharacters
- •Unicode Character Blocks
- •Using Unicode Character Blocks
- •Metacharacters Supported in W3C XML Schema
- •Positional Metacharacters
- •Matching Numeric Digits
- •Alternation
- •Using the \w and \s Metacharacters
- •Escaping Metacharacters
- •Exercises
- •Introduction to the java.util.regex Package
- •Obtaining and Installing Java
- •The Pattern Class
- •Using the matches() Method Statically
- •Two Simple Java Examples
- •The Properties (Fields) of the Pattern Class
- •The CASE_INSENSITIVE Flag
- •Using the COMMENTS Flag
- •The DOTALL Flag
- •The MULTILINE Flag
- •The UNICODE_CASE Flag
- •The UNIX_LINES Flag
- •The Methods of the Pattern Class
- •The compile() Method
- •The flags() Method
- •The matcher() Method
- •The matches() Method
- •The pattern() Method
- •The split() Method
- •The Matcher Class
- •The appendReplacement() Method
- •The appendTail() Method
- •The end() Method
- •The find() Method
- •The group() Method
- •The groupCount() Method
- •The lookingAt() Method
- •The matches() Method
- •The pattern() Method
- •The replaceAll() Method
- •The replaceFirst() Method
- •The reset() Method
- •The start() Method
- •The PatternSyntaxException Class
- •Using the \d Metacharacter
- •Character Classes
- •The POSIX Character Classes in the java.util.regex Package
- •Unicode Character Classes and Character Blocks
- •Using Escaped Characters
- •Using Methods of the String Class
- •Using the matches() Method
- •Using the replaceFirst() Method
- •Using the replaceAll() Method
- •Using the split() Method
- •Exercises
- •Obtaining and Installing Perl
- •Creating a Simple Perl Program
- •Basics of Perl Regular Expression Usage
- •Using the m// Operator
- •Using Other Regular Expression Delimiters
- •Matching Using Variable Substitution
- •Using the s/// Operator
- •Using s/// with the Global Modifier
- •Using s/// with the Default Variable
- •Using the split Operator
- •Using Quantifiers in Perl
- •Using Positional Metacharacters
- •Captured Groups in Perl
- •Using Back References in Perl
- •Using Alternation
- •Using Character Classes in Perl
- •Using Lookahead
- •Using Lookbehind
- •Escaping Metacharacters
- •A Simple Perl Regex Tester
- •Exercises
- •Index
Chapter 20
Again, the Boolean value returned by the Test() method is assigned to the MatchOrNot variable:
MatchOrNot = myRegexp.Test(TestString)
If there is a match, the MatchOrNot variable contains a value equivalent to Boolean True, so a message specifying the pattern and the match is added to the displayString variable:
If MatchOrNot Then
displayString = displayString & VBCrLf & “When the pattern is ‘“ & myRegExp.Pattern
&“‘ the input ‘“ _
&TestString & “‘ contains a match.”
But if there is no match, a message indicating that is added to the displayString variable:
Else
displayString = displayString & VBCrLf & “When the pattern is ‘“ & myRegExp.Pattern
&“‘ the input ‘“ _
&TestString & “‘ does not contain a match.” End If
Finally, the value of the displayString variable (which contains information about two attempted matches with two different values of the Pattern property) is displayed in a message box:
MsgBox displayString
End Function
When the test string is A99, it matches the pattern [A-Z]\d{2} and also matches the pattern
^[A-Z]\d{2}.
When the test string is A999, it matches the pattern [A-Z]\d{2} because there is an alphabetic character followed by two numeric digits. However, there is no match for the second pattern, ^[A-Z]\d{2}$,because there are three numeric digits, not two as required by the pattern, before the end-of-line position that matches the $ metacharacter.
The test string A2A fails to match either pattern because there is no alphabetic character followed by two numeric digits, as would be required by both patterns, [A-Z]\d{2} and ^[A-Z]\d{2}$.
Character Classes
VBScript has full support for character classes. The VBScript documentation does, however, refer to character classes as character sets.
To match any character from A through L, the character class [ABCDEFGHIJKL] can be used. Equally, a range can be used, [A-L].
Negated character classes can be used, too. The character class [^A-D] will match any character except A through D.
478
Regular Expressions and VBScript
Word Boundaries
VBScript supports the \b metacharacter to match the position either at the beginning or at the end of a sequence of word characters. Often, the sequence of alphanumeric characters will form what a human reader will view as a word, but regular expression engines do not have knowledge of the concept of a word. The \b metacharacter matches in one of two situations:
A position where the preceding character is contained in [A-Za-z0-9_] and the following character is contained in [^A-Za-z0-9_]. This is equivalent to the end of a word.
A position where the preceding character is contained in [^A-Za-z0-9_] and the following character is contained in [A-Za-z0-9_]. This is equivalent to the beginning of a word.
Lookahead
VBScript supports lookahead. Both positive and negative lookaheads are supported. The syntax for a positive lookahead is (?=theLookahead) and for a negative lookahead is (?!theNegativeLookahead).
The following example demonstrates both positive and negative lookahead. The test file,
Lookaheads.html, is shown here:
<html>
<head>
<title>Positive and Negative Lookahead</title> <script language=”vbscript” type=”text/vbscript”> Function MatchLookaheads
Dim myRegExp, TestName, Match, Matches, displayString displayString = “”
Set myRegExp = new RegExp
myRegExp.Pattern = “the(?=atre)” ‘matches, for example, the in theatre myRegExp.IgnoreCase = True
myRegExp.Global = True
TestString = InputBox(“Enter characters and numbers in the text box below.”) Set Matches = myRegexp.Execute(TestString)
displayString = displayString & “MATCH ATTEMPT 1: ‘the’ in ‘theatre’” & VBCrLf For Each Match in Matches
displayString = displayString & “Match found at position “ & Match.FirstIndex &
“.”
displayString = displayString & “The match value is ‘“ & Match.Value & “‘.” & VBCrLf
Next
displayString = displayString & VBCrLf & VBCrLf
‘Begin a new match which produces a new Match collection. myRegExp.Pattern = “the(?!atre)” ‘matches the NOT in theatre Set Matches = myRegexp.Execute(TestString)
displayString = displayString & “MATCH ATTEMPT 2: ‘the’ not in ‘theatre’” & VBCrLf For Each Match in Matches
displayString = displayString & “Match found at position “ & Match.FirstIndex &
“.”
displayString = displayString & “The match value is ‘“ & Match.Value & “‘.” & VBCrLf
479
Chapter 20
Next
MsgBox displayString
End Function
</script>
</head>
<body onload=”MatchLookaheads”>
</body>
</html>
Try It Out |
Positive and Negative Lookahead |
1.Open Lookaheads.html in Internet Explorer.
2.In the text box in the input box, enter the character sequence They love the theatre theatrically..
3.Click the OK button, and inspect the result displayed in the message box, as shown in Figure 20-15. The Match 1 section in the message box occurs when the pattern is the(?=atre). The Match 2 section in the message box occurs when the pattern is the(?!atre).
Figure 20-15
How It Works
When the page loads, the MatchLookaheads function is called:
<body onload=”MatchLookaheads”>
The code uses the RegExp object’s Execute() method twice. First, with the following value in the Pattern property:
myRegExp.Pattern = “the(?=atre)” ‘matches, for example, the in theatre
The Execute() method is executed:
Set Matches = myRegexp.Execute(TestString)
The displayString variable is assigned a label indicating that this is the first match attempt:
displayString = displayString & “MATCH ATTEMPT 1: ‘the’ in ‘theatre’” & VBCrLf
480
Regular Expressions and VBScript
For each Match object in the Matches collection (only one match in this case), information about the match is added to the displayString variable:
For Each Match in Matches
displayString = displayString & “Match found at position “ & Match.FirstIndex &
“.”
displayString = displayString & “The match value is ‘“ & Match.Value & “‘.” &
VBCrLf
‘displayString = “” Next
displayString = displayString & VBCrLf & VBCrLf
The pattern being matched is the(?=atre), which matches the character sequence the when it is followed by the character sequence atre. This is positive lookahead. It matches the in, for example, theatre or theatres.
Then the second attempt at matching is made. The value of the Pattern property is assigned a pattern that includes a negative lookahead. This means that matches will occur when the character sequence the is not followed by the character sequence atre:
myRegExp.Pattern = “the(?!atre)” ‘matches the NOT in theatre
The Execute() method means that the former Matches collection is replaced with a new one. However, information about the former Matches collection has already been captured in the displayString variable for later displaying:
Set Matches = myRegexp.Execute(TestString)
Information about the second Matches collection is now added to the displayString variable:
displayString = displayString & “MATCH ATTEMPT 2: ‘the’ not in ‘theatre’” & VBCrLf For Each Match in Matches
displayString = displayString & “Match found at position “ & Match.FirstIndex &
“.”
displayString = displayString & “The match value is ‘“ & Match.Value & “‘.” & VBCrLf
Next
The first match attempt matches the pattern the(?=atre), which includes the positive lookahead. In the test character sequence, They love the theatre theatrically., it matches the character sequence the in theatre. The Matches collection contains a single Match object.
The second match attempt matches the pattern the(?!atre), which includes the negative lookahead. In the test character sequence, They love the theatre theatrically., there are three matches. The second Matches collection, therefore, contains three Match objects corresponding to matches in The of They, the word the, and in the word theatrically. Notice that while matching is case insensitive, the case of the initial T of They is preserved.
481