- •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 23
How It Works
The original string Star Training Company is assigned to the $myString variable:
$myString = “Star Training Company.”;
The string value returned by the preg_replace() function is assigned to the $newString variable. The pattern used in the preg_replace() function is a literal pattern Star. The replacement text is Moon. Replacement is to take place in the string specified by the $myString variable. Essentially, any occurrence of Star is replaced by Moon:
$newString = preg_replace(“/Star/”, “Moon”, $myString);
The original and replaced strings are displayed to the user:
echo “<p>The original string was: ‘$myString’.</p>”;
echo “<p>After replacement the string is: ‘$newString’.</p.>”;
Using the preg_replace_callback() Function
The preg_replace_callback() function behaves essentially identically to the preg_replace() function, except that the second argument to the preg_replace_callback() function is a callback to another function. The callback can be to any user-specified function.
Using the preg_split() Function
The preg_split() function splits a test string according to a regular expression pattern. It returns an array. It takes two mandatory arguments and two optional arguments. The two mandatory arguments are a regular expression pattern and a test string. The third (optional) argument is an int value that specifies the maximum number of splits. The fourth (optional) argument is an int value that indicates the flags that are set.
Try It Out |
The preg_split() Function |
1.Type the following code in a text editor:
<html>
<head>
<title>A preg_split() Example</title> </head>
<body>
<?php
$myCSV = “Oranges, Apples, Bananas, Kiwi Fruit, Mangos”; $myArray = preg_split(“/,/”, $myCSV);
echo “<p>The original string was: ‘$myCSV’.</p>”;
echo “<p>After splitting the array contains the following values:</p.><br />”; print_r(array_values($myArray));
?>
</body>
</html>
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PHP and Regular Expressions
2.Save the code as C:\inetpub\wwwroot\PHP\preg_split.php.
3.Type the following URL in Internet Explorer: http://localhost/PHP/preg_split.php. Inspect the displayed results, as shown in Figure 23-20.
Figure 23-20
How It Works
The example splits a comma-separated list of values that are contained in a single string into an array. First, the test string is assigned to the $myCSV variable:
$myCSV = “Oranges, Apples, Bananas, Kiwi Fruit, Mangos”;
Then the array returned by the preg_split() function is assigned to the $myArray variable. The first argument to preg_split() is a regular expression pattern containing a comma, so the test string $myCSV is split at each comma. Splitting takes place at each occurrence of the comma because no third argument to the preg_split() function is specified:
$myArray = preg_split(“/,/”, $myCSV);
Two echo statements are used to display the original string and information to the user. The print_r() function is used with the array_values() function to display the values in the $myArray variable:
echo “<p>The original string was: ‘$myCSV’.</p>”;
echo “<p>After splitting the array contains the following values:</p.><br />”; print_r(array_values($myArray));
The Metacharacters Suppor ted in PHP
This description of the supported metacharacters will treat the ereg() and preg() sets of functions separately. So if you wish to use one of these sets of functions only, you can easily see which functionality is supported in your chosen set of functions.
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Chapter 23
Supported Metacharacters with ereg()
The following table summarizes the metacharacters supported in PHP when you are using the ereg() family of functions.
Metacharacter |
Description |
|
|
\d |
Not supported. Use the character class [0-9] instead. |
\D |
Not supported. Use the negated character class [^0-9] |
|
instead. |
\w |
Not supported. Use the character class [A-Za-z0-9_] or |
|
the POSIX character class [:alnum:] instead with ereg(). |
\W |
Not supported. Use the negated character class |
|
[^A-Za-z0-9_] instead with ereg(). |
? |
Quantifier. Matches zero or one occurrence of the preceding |
|
character or group. |
* |
Quantifier. Matches zero or more occurrences of the preced- |
|
ing character or group. |
+ |
Quantifier. Matches one or more occurrences of the preced- |
|
ing character or group. |
{n,m} |
Quantifier. Matches at least n occurrences and no more than |
|
m occurrences of the preceding character or group. |
. (period character) |
Matches any character except newline. |
^ |
Matches the position at the beginning of a string. |
$ |
Matches the position at the end of a string. |
[...] |
Character class. Matches a single occurrence of any charac- |
|
ter contained between the square brackets. |
[^...] |
Negated character class. Matches a single occurrence of any |
|
character not contained between the square brackets. |
|
|
Using POSIX Character Classes with PHP
The ereg() functionality is based on POSIX. Therefore, you can use POSIX character classes such as [:alnum:] with ereg() and associated functions.
The following table lists the most commonly used POSIX character classes.
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PHP and Regular Expressions |
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Character Class |
Description |
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[:alnum:] |
|
Matches alphabetic or numeric characters |
|
|
|
[:alpha:] |
|
Matches alphabetic characters |
|
|
|
[:space:] |
|
Matches whitespace characters |
|
|
|
[:blank:] |
|
Matches a space character or a tab character |
|
|
|
[:digit:] |
|
Matches a numeric digit |
|
|
|
[:lower:] |
|
Matches a lowercase alphabetic character |
|
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|
[:upper:] |
|
Matches an uppercase alphabetic character |
|
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|||
Try It Out |
|
Using [:alnum:] with ereg() |
|
||
1.Enter the following code in your favorite text editor:
<html>
<head>
<title>ereg() [:alnum:] Test</title> </head>
<body>
<?php
$match = ereg(‘[[:alnum:]]+’, “Hello world!”, $matches); if ($match)
{
echo “<p>A match was found.</p>”; echo “<p>$matches[0]</p>”;
}
?>
</body>
</html>
2.Save the file as EregAlnumTest.php.
3.In Internet Explorer, enter the URL http://localhost/PHP/EregAlnumTest.php, and inspect the displayed result, as shown in Figure 23-21.
Figure 23-21
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Chapter 23
How It Works
The POSIX character class [:alnum:] matches alphabetic characters and numeric digits. Unlike the \w metacharacter, it does not match the underscore character.
The first argument to the ereg() function matches one or more alphanumeric characters. Notice that in PHP, the [:alnum:] character class is contained inside another pair of square brackets.
Matching is attempted against the test string, Hello world!. The ereg() function has three arguments, so the value of groups in the first match, if there is one, is returned in the $matches array:
$match = ereg(‘[[:alnum:]]+’, “Hello world!”, $matches);
The if statement tests if there is a match, using the value of the $match variable:
if ($match)
In this case, the user is informed that there is a match:
{
echo “<p>A match was found.</p>”;
The matched text is contained in the zeroth group in the $matches array. That matched character sequence is displayed to the user:
echo “<p>$matches[0]</p>”;
}
The next example uses the POSIX [:space:] character class, which matches whitespace characters.
Try It Out |
Using the [:space:] Character Class |
1.Enter the following code in a text editor:
<html>
<head>
<title>ereg() [:space:] Test</title> </head>
<body>
<?php
$match = ereg(‘o[[:space:]]+w’, “Hello world!”, $matches); if ($match)
{
echo “<p>A match was found.</p>”; echo “<p>$matches[0]</p>”;
}
?>
</body>
</html>
584