- •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
Metacharacter |
Description |
|
|
* |
A quantifier. It matches when there are zero or more occurrences of |
|
the preceding character or group. |
+ |
A quantifier. It matches when there are one or more occurrences of |
|
the preceding character or group. |
{n,m} |
Quantifier notation. It matches when there is a minimum of n and a |
|
maximum of m occurrences of the preceding character or group. |
( ... ) |
Grouping parentheses. |
(?: ... ) |
Nongrouping parentheses. |
(?= ... ) |
Positive lookahead. |
(?! ... ) |
Negative lookahead. |
| |
Alternation. |
[ ... ] |
Character class. Character class ranges are supported. |
[^ ... ] |
Negated character class. |
\b |
Matches the boundary between alphanumeric characters and nonal- |
|
phanumeric characters. In effect, it can match the boundary at the |
|
beginning or end of a “word.” |
\B |
Matches a position that does not match \b. |
\d |
Matches a numeric digit. It is equivalent to the character class [0-9]. |
\D |
Matches a character that is not a numeric digit. It is equivalent to the |
|
negated character class [^0-9]. |
\s |
Matches any whitespace character. |
\S |
Matches any character that does not match \s. |
\t |
Matches a tab character. |
\w |
Matches any alphanumeric “word” character. It is equivalent to the |
|
character class [A-Za-z0-9_]. |
\W |
Matches any character that does not match \w. It is equivalent to the |
|
negated character class [^A-Za-z0-9_]. |
|
|
Quantifiers
VBScript supports a full range of quantifiers — that is, the ?, *, + metacharacters, together with the {n,m} notation.
The usage of these quantifiers in VBScript is standard.
474
Regular Expressions and VBScript
Positional Metacharacters
The ^ metacharacter is supported and matches the position before the first character of a character sequence. The $ metacharacter is also supported and matches the position after the last character of an input character sequence.
The test file, Positional.html, is shown here:
<html>
<head>
<title>Positional Metacharacters</title>
<script language=”vbscript” type=”text/vbscript”> Dim myRegExp, TestString, displayString, MatchOrNot
Function FindMatch displayString = “”
Set myRegExp = new RegExp myRegExp.Pattern = “[A-Z]\d{2}” myRegExp.IgnoreCase = False myRegExp.Global = False
TestString = InputBox(“Enter one alphabetic character and two numbers in the text box below.”)
MatchOrNot = myRegexp.Test(TestString) If MatchOrNot Then
displayString = “When the pattern is ‘“ & myRegExp.Pattern & “‘ the input ‘“ _
&TestString & “‘ contains a match.” Else
displayString = “When the pattern is ‘“ & myRegExp.Pattern & “‘ the input ‘“ _
&TestString & “‘ does not contain a match.”
End If
myRegExp.Pattern = “^[A-Z]\d{2}$” MatchOrNot = myRegexp.Test(TestString) If MatchOrNot Then
displayString = displayString & VBCrLf & “When the pattern is ‘“ & myRegExp.Pattern
&“‘ the input ‘“ _
&TestString & “‘ contains a match.” Else
displayString = displayString & VBCrLf & “When the pattern is ‘“ & myRegExp.Pattern
&“‘ the input ‘“ _
&TestString & “‘ does not contain a match.”
End If
MsgBox displayString
End Function
</script>
</head>
<body onload=”FindMatch”>
</body>
</html>
The code matches the character sequence entered into the input box against two patterns. The first does not include the positional metacharacters ^ and $. The second pattern includes both metacharacters.
475
Chapter 20
Try It Out |
Positional Metacharacters |
1.Open Positional.html in Internet Explorer.
2.In the text box in the input box, enter the character sequence A99.
3.Click the OK button, and inspect the information displayed in the message box, as shown in Figure 20-12. The message box shows the results of attempted matching when there are no positional metacharacters present and when both positional metacharacters are present. Notice that there is a match in both situations.
Figure 20-12
4.Click the OK button to dismiss the message box and then press F5 to reload the Web page.
5.In the text box in the input box, enter the character sequence A999.
6.Click the OK button, and inspect the information displayed in the message box, as shown in Figure 20-13. Notice that there is a match when no positional metacharacters are present but no match when the positional metacharacters are present in the pattern.
Figure 20-13
7.Click the OK button to dismiss the message box and then press F5 to reload the Web page.
8.In the text box in the input box, enter the character sequence A2A.
9.Click the OK button, and inspect the information displayed in the message box, as shown in Figure 20-14. There is no match with either pattern.
Figure 20-14
476
Regular Expressions and VBScript
How It Works
When the page is loaded, the FindMatch function is called:
<body onload=”FindMatch”>
The FindMatch function twice uses the RegExp object’s Test() method to attempt to match a string input by the user.
Initially, the value assigned to the Pattern property is the pattern [A-Z]\d{2}, which matches a single alphabetic character followed by two numeric digits:
myRegExp.Pattern = “[A-Z]\d{2}”
Because the IgnoreCase and Global properties are each set to False, the alphabetic character can be entered in either case, and only one match is attempted:
myRegExp.IgnoreCase = False
myRegExp.Global = False
The string that is input by the user is assigned to the TestString variable:
TestString = InputBox(“Enter one alphabetic character and two numbers in the text
box below.”)
And the result of the Test() method, with the TestString variable as its argument, is assigned to the variable MatchOrNot, which contains a Boolean value. The MatchOrNot variable either contains a nonzero length string (which is equivalent to Boolean True) or the empty string (which is equivalent to the Boolean value False):
MatchOrNot = myRegexp.Test(TestString)
If there is a match, the pattern is output together with the test string it matches:
If MatchOrNot |
Then |
|
displayString |
= “When the pattern is ‘“ & myRegExp.Pattern & “‘ the input ‘“ _ |
|
& TestString |
& “‘ |
contains a match.” |
|
|
|
If there is no match, a message that the pattern is not matched by the input string is output:
Else
displayString = “When the pattern is ‘“ & myRegExp.Pattern & “‘ the input ‘“ _
& TestString & “‘ does not contain a match.” End If
The displayString variable now contains the result of the first attempted matching process. Now, however, the value of the Pattern property is changed to allow a second attempted match using a pattern that now includes both the ^ and $ metacharacters:
myRegExp.Pattern = “^[A-Z]\d{2}$”
477