- •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
and splitting are to take place. In the absence of a third argument, matching and splitting proceed through the whole string.
The sql_regcase() Function
The sql_regcase() function is different from all the other functions in the ereg() family because it is used to create a regular expression pattern, rather than use one, as all the other functions do.
Try It Out |
Using the sql_regcase() Function |
1.Type the following code in a text editor:
<html>
<head>
<title>sql_regcase() Demo</title> </head>
<body>
<?php
$sequenceToMatch = “Doctor”;
$myPattern = sql_regcase($sequenceToMatch);
echo “<p>To match ‘$sequenceToMatch’ the sql_regcase() function produces: ‘$myPattern’.</p>”;
?>
</body>
</html>
2.Save the code as C:\inetpub\wwwroot\PHP\sql_regcaseDemo.php.
3.In Internet Explorer, enter the URL http://localhost/PHP/sql_regcaseDemo.php, and inspect the displayed results, as shown in Figure 23-12. The result produced is a sequence of character classes that allow case-insensitive matching.
Figure 23-12
How It Works
For each character in $sequenceToMatch a character class containing both an uppercase and lowercase character is created. So, for example, for the D of doctor, a character class [Dd] is created.
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Chapter 23
Perl Compatible Regular Expressions
Perl Compatible Regular Expressions (PCRE) provides more modern and more powerful regular expression support in PHP than do ereg() and associated functions.
The following table summarizes the family of functions supported in PCRE in PHP. Each of these functions is covered in more detail a little later in the chapter.
Function |
Description |
|
|
preg_match() |
Attempts to match a specified pattern in a specified test string |
preg_match_all() |
Attempts to match a specified pattern as many times as possi- |
|
ble in a specified test string |
preg_grep() |
This function finds matches for a regular expression pattern in |
|
an array |
preg_quote() |
This function takes a regular expression pattern and escapes |
|
each character in it using a backslash |
preg_replace() |
Attempts to match a regular expression pattern in a string and |
|
replaces any matches using a specified replacement string |
preg_replace_callback() |
Similar to preg_replace(), except that a callback is used to |
|
define the replacement string |
preg_split() |
Splits a test string into an array of substrings, using a specified |
|
pattern to define where splitting should take place |
|
|
Pattern Delimiters in PCRE
PCRE includes support for developer-specified delimiters of regular expression patterns. The default delimiters are paired forward-slash characters. To supply a regular expression, you enclose it in paired delimiters inside the paired double quotes.
You can use any paired nonalphanumeric character as a delimiter, or you can use matched characters such as {}, <>, or ().
Try It Out |
Various Delimiters |
1.Type the following code into a text editor:
<html>
<head>
<title>Simple preg_match() Regex Test</title> </head>
<body>
<?php
if (preg_match(“/Hel/”, “Hello world!”)) echo “<p>A match was found using paired ‘/’ as delimiter.</p>”;
if (preg_match(“.Hel.”, “Hello world!”)) echo “<p>A match was found using paired ‘.’ as delimiter.</p>”;
568
PHP and Regular Expressions
if (preg_match(“{Hel}”, “Hello world!”)) echo “<p>A match was found using matched ‘{‘ and ‘}’ as delimiters.</p>”;
if (preg_match(“(Hel)”, “Hello world!”)) echo “<p>A match was found using matched ‘(‘ and ‘)’ as delimiters.</p>”;
if (preg_match(“<Hel>”, “Hello world!”)) echo “<p>A match was found using matched ‘<’ and ‘>’ as delimiters.</p>”;
?>
</body>
</html>
2.Save the code as C:\inetpub\wwwroot\PHP\DelimiterTest.php.
3.Type the URL http://localhost/PHP/DelimiterTest.php into Internet Explorer, and inspect the displayed results, as shown in Figure 23-13.
Figure 23-13
How It Works
There are five examples of using the preg_match() function in this example. Each does basically the same thing, testing whether there is a match for the literal pattern Hel in the test string Hello world!, and if there is (there is in each of the examples), a message stating that there is a match and what delimiter was used is displayed.
The first example uses paired forward slashes as delimiters. I prefer using these because they are the default delimiters in Perl too:
if (preg_match(“/Hel/”, “Hello world!”)) echo “<p>A match was found using paired
‘/’ as delimiter.</p>”;
However, you can also use other paired nonalphanumeric delimiters. The second example uses paired period characters as the pattern delimiters:
if (preg_match(“.Hel.”, “Hello world!”)) echo “<p>A match was found using paired
‘.’ as delimiter.</p>”;
569
Chapter 23
The other three examples use matched pairs of characters. They are matched in the sense that a left curly brace, {, is matched with a right curly brace, }. The other matched pairs are ordinary parentheses, ( and ), and left and right angled brackets, < and >.
if (preg_match(“{Hel}”, “Hello world!”)) echo “<p>A match was found using matched ‘{‘ and ‘}’ as delimiters.</p>”;
if (preg_match(“(Hel)”, “Hello world!”)) echo “<p>A match was found using matched
‘(‘ and ‘)’ as delimiters.</p>”;
if (preg_match(“<Hel>”, “Hello world!”)) echo “<p>A match was found using matched ‘<’ and ‘>’ as delimiters.</p>”;
I suggest that unless there is good reason to vary from using the forward slash, you use that. Most developers will be familiar with the use of paired forward slashes as regular expression delimiters, so using them is least likely to cause confusion for others reading your code. If you use another delimiter, I suggest that you add a comment to document your choice for any developer who has to maintain your code.
Escaping Pattern Delimiters
When a character such as the forward slash is used as a regular expression pattern delimiter in PHP, it is necessary to escape that delimiter character if you desire to match that character literally. For example, if the forward slash is used as a pattern delimiter, and you want to match an HTTP URL that references the com, net, org, info, and biz top-level domains, you must escape each forward slash in the pattern, which is the first argument of the preg_match() function. For example:
preg_match(‘/http:\/\/.*\.(com|net|org|info|biz)\/.*/’, $testString)
Matching Modifiers in PCRE
It will come as little surprise that the matching modifiers in Perl Compatible Regular Expressions are based on those in Perl. The following table summarizes the matching modifiers available in the PCRE functionality in PHP.
Matching Modifier |
Description |
|
|
i |
Causes matching to be case insensitive. |
m |
Multiline. Alters the effect of the ^ and $ metacharacters. With multi- |
|
line chosen, ^ matches the position at the beginning of a line, and $ |
|
matches the position at the end of a line. |
s |
Modifies what the period metacharacter matches. With the s modi- |
|
fier selected, the period metacharacter matches all characters. With- |
|
out s being selected, the period metacharacter matches all characters |
|
except newline. |
x |
Modifies how whitespace inside a pattern is processed. With x |
|
selected unescaped, whitespace characters are ignored. |
A |
Constrains matching to the beginning of the test string. |
D |
If the D modifier is set, the $ metacharacter matches only at the end |
|
of the test string. If the m matching modifier is set, the D modifier is |
|
ignored. |
|
|
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