- •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
PHP and Regular Expressions
The eregi_replace() Function
The eregi_replace() function matches in a case-insensitive way and replaces any match found in the test string using the replacement string.
The eregi_replace() function takes three arguments. The first is a string value that represents the regular expression pattern. The second is the replacement string that replaces each match found in the test string. The third argument is the test string.
Try It Out |
Using the eregi_replace() Function |
1.Enter the following code in a text editor:
<html>
<head>
<title>eregi_replace() Demo</title> </head>
<body>
<?php
$myPattern = “Doctor”; $myReplacement = “Dr.”;
$myString = “Doctor Smith spoke with another doctor.”; echo “<p>The original string was ‘$myString’.</p>”; echo “<p>The pattern is ‘$myPattern’.</p>”;
echo “<p>The replacement text is ‘$myReplacement’.</p>”; $replacedString = eregi_replace($myPattern, $myReplacement, $myString); $displayString = “<p>After replacment the string becomes: ‘ “; $displayString = $displayString . $replacedString . “‘.</p>”;
echo $displayString; ?>
</body>
</html>
2.Save the code as C:\inetpub\wwwroot\PHP\eregi_replaceDemo.php.
3.In Internet Explorer, enter the URL http://localhost/PHP/eregi_replaceDemo.php, and inspect the displayed results, as shown in Figure 23-10. Notice that two occurrences of the word Doctor (one Doctor and the other doctor) have been replaced. In all likelihood, it would be undesirable to replace the second occurrence.
Figure 23-10
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How It Works
The example aims to replace all occurrences of the string Doctor, matched case insensitively, with the abbreviated form Dr..
You first assign values to the variables $myPattern, $myReplacement, and $myString:
$myPattern = “Doctor”; $myReplacement = “Dr.”;
$myString = “Doctor Smith spoke with another doctor.”;
After displaying the values of the preceding variables to the user, the eregi_replace() function is used to replace all occurrences of Doctor, matched case insensitively, with the form Dr.:
$replacedString = eregi_replace($myPattern, $myReplacement, $myString);
This causes the occurrences of Doctor and doctor (in the test string) to be replaced, because matching against the pattern Doctor is case insensitive. This reduces the specificity of matching because character sequences such as DocTOr, dOCtor, and so on would also be matched. In all likelihood, the replacing of doctor by Dr. is inappropriate. For this particular task, the case-sensitive matching of the ereg_replace() function would have been more appropriate. However, the example does demonstrate how case-insensitive matching works.
The split() Function
The split() function can split a string into component substrings, with the point where the string is split determined by a regular expression pattern. This can be useful when handling comma-separated values in files or handling dates that have different separators. The following example illustrates how the split() function can be used to split dates that use the hyphen, forward slash, and period character as separators.
The split() function can take two or three arguments. The first argument is the regular expression pattern at which a split is to take place. If a match is found, the character sequence that matches the pattern is discarded. This makes sense as default behavior when, for example, you have comma-separated data and want only the data and not the commas. The second argument is the test string. The third (optional) argument is an int value, which specifies the maximum number of times matching and splitting is to take place.
Try It Out |
Using the split() Function |
1.Type the following code into a code editor:
<html>
<head>
<title>split() Function Demo</title> </head>
<body>
<?php
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PHP and Regular Expressions
$myString1 = “2004/09/23”; $myString2 = “2004.09.23”; $myString3 = “2004-09-23”; $myPattern = “[-/.]”;
list($year, $month, $day) = split($myPattern, $myString1);
echo “<p>String was: $myString1. <br />Year: $year <br />Month: $month <br />Day: $day</p>”;
list($year, $month, $day) = split($myPattern, $myString2);
echo “<br /><br /><p>String was: $myString2. <br />Year: $year <br />Month: $month <br />Day: $day</p>”;
list($year, $month, $day) = split($myPattern, $myString3);
echo “<br /><br /><p>String was: $myString3. <br />Year: $year <br />Month: $month <br />Day: $day</p>”;
?>
</body>
</html>
2.Save the code as C:\inetpub\wwwroot\PHP\splitdemo.php.
3.In Internet Explorer, type the URL http://localhost/PHP/splitdemo.php, and inspect the displayed results, as shown in Figure 23-11.
Figure 23-11
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Chapter 23
How It Works
This example demonstrates how three strings, which represent dates, can be split using three possible separators: the forward slash, the period character, and the hyphen.
First, three variables are declared, each of which holds the date September 23, 2004. Each of the variables — $myString1, $myString2, and $myString3 — uses a different separator character.
$myString1 = “2004/09/23”; $myString2 = “2004.09.23”; $myString3 = “2004-09-23”;
Then the variable $myPattern is declared and is assigned a string that represents a character class containing the hyphen, the forward slash, and the period character. The hyphen character is the first character in the character class, so this is not specifying a character class range:
$myPattern = “[-/.]”;
A list is created, containing the component parts of the date represented in myString1. The forward slash in the character class [-/.] matches twice, so the string myString1 is split into three parts, which are represented in the list by $year, $month, and $day:
list($year, $month, $day) = split($myPattern, $myString1);
The variables $year, $month, and $day are output:
echo “<p>String was: $myString1. <br />Year: $year <br />Month: $month <br />Day:
$day</p>”;
The process of creating a list that contains the component parts of a string is repeated with the variables $myString2 (which uses a period character as separator) and $myString3 (which uses a hyphen as separator):
list($year, $month, $day) = split($myPattern, $myString2);
echo “<br /><br /><p>String was: $myString2. <br />Year: $year <br />Month: $month <br />Day: $day</p>”;
list($year, $month, $day) = split($myPattern, $myString3);
echo “<br /><br /><p>String was: $myString3. <br />Year: $year <br />Month: $month <br />Day: $day</p>”;
The spliti() Function
The spliti() function does the same thing as the split() function, except that it matches case insensitively. If an alphabetic character is used as a separator, spliti() will match case insensitively, while split() matches case sensitively. However, because the most likely separators used are the comma, the hyphen, the forward slash, the semicolon, and the period character, the two functions will often behave identically in practical use.
The spliti() function, like the split() function, takes two or three arguments. The first argument is the regular expression pattern at which splitting is to take place. The second argument is the test string. The third (optional) argument is an int value, which specifies the maximum number of times matching
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