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Chapter 1. Strings
Introduction
Recipe 1.1 Accessing Substrings
Recipe 1.2 Establishing a Default Value
Recipe 1.3 Exchanging Values Without Using Temporary Variables
Recipe 1.4 Converting Between Characters and Values
Recipe 1.5 Using Named Unicode Characters
Recipe 1.6 Processing a String One Character at a Time
Recipe 1.7 Reversing a String by Word or Character
Recipe 1.8 Treating Unicode Combined Characters as Single Characters
Recipe 1.9 Canonicalizing Strings with Unicode Combined Characters
Recipe 1.10 Treating a Unicode String as Octets
Recipe 1.11 Expanding and Compressing Tabs
Recipe 1.12 Expanding Variables in User Input
Recipe 1.13 Controlling Case
Recipe 1.14 Properly Capitalizing a Title or Headline
Recipe 1.15 Interpolating Functions and Expressions Within Strings
Recipe 1.16 Indenting Here Documents
Recipe 1.17 Reformatting Paragraphs
Recipe 1.18 Escaping Characters
Recipe 1.19 Trimming Blanks from the Ends of a String
Recipe 1.20 Parsing Comma-Separated Data
Recipe 1.21 Constant Variables
Recipe 1.22 Soundex Matching
Recipe 1.23 Program: fixstyle
Recipe 1.24 Program: psgrep
Chapter 2. Numbers
Introduction
Recipe 2.1 Checking Whether a String Is a Valid Number
Recipe 2.2 Rounding Floating-Point Numbers
Recipe 2.3 Comparing Floating-Point Numbers
Recipe 2.4 Operating on a Series of Integers
Recipe 2.5 Working with Roman Numerals
Recipe 2.6 Generating Random Numbers
Recipe 2.7 Generating Repeatable Random Number Sequences
Recipe 2.8 Making Numbers Even More Random
Recipe 2.9 Generating Biased Random Numbers
Recipe 2.10 Doing Trigonometry in Degrees, Not Radians
Recipe 2.11 Calculating More Trigonometric Functions
Recipe 2.12 Taking Logarithms
Recipe 2.13 Multiplying Matrices
Recipe 2.14 Using Complex Numbers
Recipe 2.15 Converting Binary, Octal, and Hexadecimal Numbers
Recipe 2.16 Putting Commas in Numbers
Recipe 2.17 Printing Correct Plurals
Recipe 2.18 Program: Calculating Prime Factors
Chapter 3. Dates and Times
Introduction
Recipe 3.1 Finding Today's Date
Recipe 3.2 Converting DMYHMS to Epoch Seconds
Recipe 3.3 Converting Epoch Seconds to DMYHMS
Recipe 3.4 Adding to or Subtracting from a Date
Recipe 3.5 Difference of Two Dates
Recipe 3.6 Day in a Week/Month/Year or Week Number
Recipe 3.7 Parsing Dates and Times from Strings
Recipe 3.8 Printing a Date
Recipe 3.9 High-Resolution Timers
Recipe 3.10 Short Sleeps
Recipe 3.11 Program: hopdelta
Chapter 4. Arrays
Introduction
Recipe 4.1 Specifying a List in Your Program
Recipe 4.2 Printing a List with Commas
Recipe 4.3 Changing Array Size
Recipe 4.4 Implementing a Sparse Array
Recipe 4.5 Iterating Over an Array
Recipe 4.6 Iterating Over an Array by Reference
Recipe 4.7 Extracting Unique Elements from a List
Recipe 4.8 Finding Elements in One Array but Not Another
Recipe 4.9 Computing Union, Intersection, or Difference of Unique Lists
Recipe 4.10 Appending One Array to Another
Recipe 4.11 Reversing an Array
Recipe 4.12 Processing Multiple Elements of an Array
Recipe 4.13 Finding the First List Element That Passes a Test
Recipe 4.14 Finding All Elements in an Array Matching Certain Criteria
Recipe 4.15 Sorting an Array Numerically
Recipe 4.16 Sorting a List by Computable Field
Recipe 4.17 Implementing a Circular List
Recipe 4.18 Randomizing an Array
Recipe 4.19 Program: words
Recipe 4.20 Program: permute
Chapter 5. Hashes
Introduction
Recipe 5.1 Adding an Element to a Hash
Recipe 5.2 Testing for the Presence of a Key in a Hash
Recipe 5.3 Creating a Hash with Immutable Keys or Values
Recipe 5.4 Deleting from a Hash
Recipe 5.5 Traversing a Hash
Recipe 5.6 Printing a Hash
Recipe 5.7 Retrieving from a Hash in Insertion Order
Recipe 5.8 Hashes with Multiple Values per Key
Recipe 5.9 Inverting a Hash
Recipe 5.10 Sorting a Hash
Recipe 5.11 Merging Hashes
Recipe 5.12 Finding Common or Different Keys in Two Hashes
Recipe 5.13 Hashing References
Recipe 5.14 Presizing a Hash
Recipe 5.15 Finding the Most Common Anything
Recipe 5.16 Representing Relationships Between Data
Recipe 5.17 Program: dutree
Chapter 6. Pattern Matching
Introduction
Recipe 6.1 Copying and Substituting Simultaneously
Recipe 6.2 Matching Letters
Recipe 6.3 Matching Words
Recipe 6.4 Commenting Regular Expressions
Recipe 6.5 Finding the Nth Occurrence of a Match
Recipe 6.6 Matching Within Multiple Lines
Recipe 6.7 Reading Records with a Separator
Recipe 6.8 Extracting a Range of Lines
Recipe 6.9 Matching Shell Globs as Regular Expressions
Recipe 6.10 Speeding Up Interpolated Matches
Recipe 6.11 Testing for a Valid Pattern
Recipe 6.12 Honoring Locale Settings in Regular Expressions
Recipe 6.13 Approximate Matching
Recipe 6.14 Matching from Where the Last Pattern Left Off
Recipe 6.15 Greedy and Non-Greedy Matches
Recipe 6.16 Detecting Doubled Words
Recipe 6.17 Matching Nested Patterns
Recipe 6.18 Expressing AND, OR, and NOT in a Single Pattern
Recipe 6.19 Matching a Valid Mail Address
Recipe 6.20 Matching Abbreviations
Recipe 6.21 Program: urlify
Recipe 6.22 Program: tcgrep
Recipe 6.23 Regular Expression Grab Bag
Chapter 7. File Access
Introduction
Recipe 7.1 Opening a File
Recipe 7.2 Opening Files with Unusual Filenames
Recipe 7.3 Expanding Tildes in Filenames
Recipe 7.4 Making Perl Report Filenames in Error Messages
Recipe 7.5 Storing Filehandles into Variables
Recipe 7.6 Writing a Subroutine That Takes Filehandles as Built-ins Do
Recipe 7.7 Caching Open Output Filehandles
Recipe 7.8 Printing to Many Filehandles Simultaneously
Recipe 7.9 Opening and Closing File Descriptors by Number
Recipe 7.10 Copying Filehandles
Recipe 7.11 Creating Temporary Files
Recipe 7.12 Storing a File Inside Your Program Text
Recipe 7.13 Storing Multiple Files in the DATA Area
Recipe 7.14 Writing a Unix-Style Filter Program
Recipe 7.15 Modifying a File in Place with a Temporary File
Recipe 7.16 Modifying a File in Place with the -i Switch
Recipe 7.17 Modifying a File in Place Without a Temporary File
Recipe 7.18 Locking a File
Recipe 7.19 Flushing Output
Recipe 7.20 Doing Non-Blocking I/O
Recipe 7.21 Determining the Number of Unread Bytes
Recipe 7.22 Reading from Many Filehandles Without Blocking
Recipe 7.23 Reading an Entire Line Without Blocking
Recipe 7.24 Program: netlock
Recipe 7.25 Program: lockarea
Chapter 8. File Contents
Introduction
Recipe 8.1 Reading Lines with Continuation Characters
Recipe 8.2 Counting Lines (or Paragraphs or Records) in a File
Recipe 8.3 Processing Every Word in a File
Recipe 8.4 Reading a File Backward by Line or Paragraph
Recipe 8.5 Trailing a Growing File
Recipe 8.6 Picking a Random Line from a File
Recipe 8.7 Randomizing All Lines
Recipe 8.8 Reading a Particular Line in a File
Recipe 8.9 Processing Variable-Length Text Fields
Recipe 8.10 Removing the Last Line of a File
Recipe 8.11 Processing Binary Files
Recipe 8.12 Using Random-Access I/O
Recipe 8.13 Updating a Random-Access File
Recipe 8.14 Reading a String from a Binary File
Recipe 8.15 Reading Fixed-Length Records
Recipe 8.16 Reading Configuration Files
Recipe 8.17 Testing a File for Trustworthiness
Recipe 8.18 Treating a File as an Array
Recipe 8.19 Setting the Default I/O Layers
Recipe 8.20 Reading or Writing Unicode from a Filehandle
Recipe 8.21 Converting Microsoft Text Files into Unicode
Recipe 8.22 Comparing the Contents of Two Files
Recipe 8.23 Pretending a String Is a File
Recipe 8.24 Program: tailwtmp
Recipe 8.25 Program: tctee
Recipe 8.26 Program: laston
Recipe 8.27 Program: Flat File Indexes
Chapter 9. Directories
Introduction
Recipe 9.1 Getting and Setting Timestamps
Recipe 9.2 Deleting a File
Recipe 9.3 Copying or Moving a File
Recipe 9.4 Recognizing Two Names for the Same File
Recipe 9.5 Processing All Files in a Directory
Recipe 9.6 Globbing, or Getting a List of Filenames Matching a Pattern
Recipe 9.7 Processing All Files in a Directory Recursively
Recipe 9.8 Removing a Directory and Its Contents
Recipe 9.9 Renaming Files
Recipe 9.10 Splitting a Filename into Its Component Parts
Recipe 9.11 Working with Symbolic File Permissions Instead of Octal Values
Recipe 9.12 Program: symirror
Recipe 9.13 Program: lst
Chapter 10. Subroutines
Introduction
Recipe 10.1 Accessing Subroutine Arguments
Recipe 10.2 Making Variables Private to a Function
Recipe 10.3 Creating Persistent Private Variables
Recipe 10.4 Determining Current Function Name
Recipe 10.5 Passing Arrays and Hashes by Reference
Recipe 10.6 Detecting Return Context
Recipe 10.7 Passing by Named Parameter
Recipe 10.8 Skipping Selected Return Values
Recipe 10.9 Returning More Than One Array or Hash
Recipe 10.10 Returning Failure
Recipe 10.11 Prototyping Functions
Recipe 10.12 Handling Exceptions
Recipe 10.13 Saving Global Values
Recipe 10.14 Redefining a Function
Recipe 10.15 Trapping Undefined Function Calls with AUTOLOAD
Recipe 10.16 Nesting Subroutines
Recipe 10.17 Writing a Switch Statement
Recipe 10.18 Program: Sorting Your Mail
Chapter 11. References and Records
Introduction
Recipe 11.1 Taking References to Arrays
Recipe 11.2 Making Hashes of Arrays
Recipe 11.3 Taking References to Hashes
Recipe 11.4 Taking References to Functions
Recipe 11.5 Taking References to Scalars
Recipe 11.6 Creating Arrays of Scalar References
Recipe 11.7 Using Closures Instead of Objects
Recipe 11.8 Creating References to Methods
Recipe 11.9 Constructing Records
Recipe 11.10 Reading and Writing Hash Records to Text Files
Recipe 11.11 Printing Data Structures
Recipe 11.12 Copying Data Structures
Recipe 11.13 Storing Data Structures to Disk
Recipe 11.14 Transparently Persistent Data Structures
Recipe 11.15 Coping with Circular Data Structures Using Weak References
Recipe 11.16 Program: Outlines
Recipe 11.17 Program: Binary Trees
Chapter 12. Packages, Libraries, and Modules
Introduction
Recipe 12.1 Defining a Module's Interface
Recipe 12.2 Trapping Errors in require or use
Recipe 12.3 Delaying use Until Runtime
Recipe 12.4 Making Variables Private to a Module
Recipe 12.5 Making Functions Private to a Module
Recipe 12.6 Determining the Caller's Package
Recipe 12.7 Automating Module Cleanup
Recipe 12.8 Keeping Your Own Module Directory
Recipe 12.9 Preparing a Module for Distribution
Recipe 12.10 Speeding Module Loading with SelfLoader
Recipe 12.11 Speeding Up Module Loading with Autoloader
Recipe 12.12 Overriding Built-in Functions
Recipe 12.13 Overriding a Built-in Function in All Packages
Recipe 12.14 Reporting Errors and Warnings Like Built-ins
Recipe 12.15 Customizing Warnings
Recipe 12.16 Referring to Packages Indirectly
Recipe 12.17 Using h2ph to Translate C #include Files
Recipe 12.18 Using h2xs to Make a Module with C Code
Recipe 12.19 Writing Extensions in C with Inline::C
Recipe 12.20 Documenting Your Module with Pod
Recipe 12.21 Building and Installing a CPAN Module
Recipe 12.22 Example: Module Template
Recipe 12.23 Program: Finding Versions and Descriptions of Installed Modules
Chapter 13. Classes, Objects, and Ties
Introduction
Recipe 13.1 Constructing an Object
Recipe 13.2 Destroying an Object
Recipe 13.3 Managing Instance Data
Recipe 13.4 Managing Class Data
Recipe 13.5 Using Classes as Structs
Recipe 13.6 Cloning Constructors
Recipe 13.7 Copy Constructors
Recipe 13.8 Invoking Methods Indirectly
Recipe 13.9 Determining Subclass Membership
Recipe 13.10 Writing an Inheritable Class
Recipe 13.11 Accessing Overridden Methods
Recipe 13.12 Generating Attribute Methods Using AUTOLOAD
Recipe 13.13 Coping with Circular Data Structures Using Objects
Recipe 13.14 Overloading Operators
Recipe 13.15 Creating Magic Variables with tie
Chapter 14. Database Access
Introduction
Recipe 14.1 Making and Using a DBM File
Recipe 14.2 Emptying a DBM File
Recipe 14.3 Converting Between DBM Files
Recipe 14.4 Merging DBM Files
Recipe 14.5 Sorting Large DBM Files
Recipe 14.6 Storing Complex Data in a DBM File
Recipe 14.7 Persistent Data
Recipe 14.8 Saving Query Results to Excel or CSV
Recipe 14.9 Executing an SQL Command Using DBI
Recipe 14.10 Escaping Quotes
Recipe 14.11 Dealing with Database Errors
Recipe 14.12 Repeating Queries Efficiently
Recipe 14.13 Building Queries Programmatically
Recipe 14.14 Finding the Number of Rows Returned by a Query
Recipe 14.15 Using Transactions
Recipe 14.16 Viewing Data One Page at a Time
Recipe 14.17 Querying a CSV File with SQL
Recipe 14.18 Using SQL Without a Database Server
Recipe 14.19 Program: gghGrep Netscape Global History
Chapter 15. Interactivity
Introduction
Recipe 15.1 Parsing Program Arguments
Recipe 15.2 Testing Whether a Program Is Running Interactively
Recipe 15.3 Clearing the Screen
Recipe 15.4 Determining Terminal or Window Size
Recipe 15.5 Changing Text Color
Recipe 15.6 Reading Single Characters from the Keyboard
Recipe 15.7 Ringing the Terminal Bell
Recipe 15.8 Using POSIX termios
Recipe 15.9 Checking for Waiting Input
Recipe 15.10 Reading Passwords
Recipe 15.11 Editing Input
Recipe 15.12 Managing the Screen
Recipe 15.13 Controlling Another Program with Expect
Recipe 15.14 Creating Menus with Tk
Recipe 15.15 Creating Dialog Boxes with Tk
Recipe 15.16 Responding to Tk Resize Events
Recipe 15.17 Removing the DOS Shell Window with Windows Perl/Tk
Recipe 15.18 Graphing Data
Recipe 15.19 Thumbnailing Images
Recipe 15.20 Adding Text to an Image
Recipe 15.21 Program: Small termcap Program
Recipe 15.22 Program: tkshufflepod
Recipe 15.23 Program: graphbox
Chapter 16. Process Management and Communication
Introduction
Recipe 16.1 Gathering Output from a Program
Recipe 16.2 Running Another Program
Recipe 16.3 Replacing the Current Program with a Different One
Recipe 16.4 Reading or Writing to Another Program
Recipe 16.5 Filtering Your Own Output
Recipe 16.6 Preprocessing Input
Recipe 16.7 Reading STDERR from a Program
Recipe 16.8 Controlling Input and Output of Another Program
Recipe 16.9 Controlling the Input, Output, and Error of Another Program
Recipe 16.10 Communicating Between Related Processes
Recipe 16.11 Making a Process Look Like a File with Named Pipes
Recipe 16.12 Sharing Variables in Different Processes
Recipe 16.13 Listing Available Signals
Recipe 16.14 Sending a Signal
Recipe 16.15 Installing a Signal Handler
Recipe 16.16 Temporarily Overriding a Signal Handler
Recipe 16.17 Writing a Signal Handler
Recipe 16.18 Catching Ctrl-C
Recipe 16.19 Avoiding Zombie Processes
Recipe 16.20 Blocking Signals
Recipe 16.21 Timing Out an Operation
Recipe 16.22 Turning Signals into Fatal Errors
Recipe 16.23 Program: sigrand
Chapter 17. Sockets
Introduction
Recipe 17.1 Writing a TCP Client
Recipe 17.2 Writing a TCP Server
Recipe 17.3 Communicating over TCP
Recipe 17.4 Setting Up a UDP Client
Recipe 17.5 Setting Up a UDP Server
Recipe 17.6 Using Unix Domain Sockets
Recipe 17.7 Identifying the Other End of a Socket
Recipe 17.8 Finding Your Own Name and Address
Recipe 17.9 Closing a Socket After Forking
Recipe 17.10 Writing Bidirectional Clients
Recipe 17.11 Forking Servers
Recipe 17.12 Pre-Forking Servers
Recipe 17.13 Non-Forking Servers
Recipe 17.14 Multitasking Server with Threads
Recipe 17.15 Writing a Multitasking Server with POE
Recipe 17.16 Writing a Multihomed Server
Recipe 17.17 Making a Daemon Server
Recipe 17.18 Restarting a Server on Demand
Recipe 17.19 Managing Multiple Streams of Input
Recipe 17.20 Program: backsniff
Recipe 17.21 Program: fwdport
Chapter 18. Internet Services
Introduction
Recipe 18.1 Simple DNS Lookups
Recipe 18.2 Being an FTP Client
Recipe 18.3 Sending Mail
Recipe 18.4 Reading and Posting Usenet News Messages
Recipe 18.5 Reading Mail with POP3
Recipe 18.6 Simulating Telnet from a Program
Recipe 18.7 Pinging a Machine
Recipe 18.8 Accessing an LDAP Server
Recipe 18.9 Sending Attachments in Mail
Recipe 18.10 Extracting Attachments from Mail
Recipe 18.11 Writing an XML-RPC Server
Recipe 18.12 Writing an XML-RPC Client
Recipe 18.13 Writing a SOAP Server
Recipe 18.14 Writing a SOAP Client
Recipe 18.15 Program: rfrm
Recipe 18.16 Program: expn and vrfy
Chapter 19. CGI Programming
Introduction
Recipe 19.1 Writing a CGI Script
Recipe 19.2 Redirecting Error Messages
Recipe 19.3 Fixing a 500 Server Error
Recipe 19.4 Writing a Safe CGI Program
Recipe 19.5 Executing Commands Without Shell Escapes
Recipe 19.6 Formatting Lists and Tables with HTML Shortcuts
Recipe 19.7 Redirecting to a Different Location
Recipe 19.8 Debugging the Raw HTTP Exchange
Recipe 19.9 Managing Cookies
Recipe 19.10 Creating Sticky Widgets
Recipe 19.11 Writing a Multiscreen CGI Script
Recipe 19.12 Saving a Form to a File or Mail Pipe
Recipe 19.13 Program: chemiserie
Chapter 20. Web Automation
Introduction
Recipe 20.1 Fetching a URL from a Perl Script
Recipe 20.2 Automating Form Submission
Recipe 20.3 Extracting URLs
Recipe 20.4 Converting ASCII to HTML
Recipe 20.5 Converting HTML to ASCII
Recipe 20.6 Extracting or Removing HTML Tags
Recipe 20.7 Finding Stale Links
Recipe 20.8 Finding Fresh Links
Recipe 20.9 Using Templates to Generate HTML
Recipe 20.10 Mirroring Web Pages
Recipe 20.11 Creating a Robot
Recipe 20.12 Parsing a Web Server Log File
Recipe 20.13 Processing Server Logs
Recipe 20.14 Using Cookies
Recipe 20.15 Fetching Password-Protected Pages
Recipe 20.16 Fetching https:// Web Pages
Recipe 20.17 Resuming an HTTP GET
Recipe 20.18 Parsing HTML
Recipe 20.19 Extracting Table Data
Recipe 20.20 Program: htmlsub
Recipe 20.21 Program: hrefsub
Chapter 21. mod_perl
Introduction
Recipe 21.1 Authenticating
Recipe 21.2 Setting Cookies
Recipe 21.3 Accessing Cookie Values
Recipe 21.4 Redirecting the Browser
Recipe 21.5 Interrogating Headers
Recipe 21.6 Accessing Form Parameters
Recipe 21.7 Receiving Uploaded Files
Recipe 21.8 Speeding Up Database Access
Recipe 21.9 Customizing Apache's Logging
Recipe 21.10 Transparently Storing Information in URLs
Recipe 21.11 Communicating Between mod_perl and PHP
Recipe 21.12 Migrating from CGI to mod_perl
Recipe 21.13 Sharing Information Between Handlers
Recipe 21.14 Reloading Changed Modules
Recipe 21.15 Benchmarking a mod_perl Application
Recipe 21.16 Templating with HTML::Mason
Recipe 21.17 Templating with Template Toolkit
Chapter 22. XML
Introduction
Recipe 22.1 Parsing XML into Data Structures
Recipe 22.2 Parsing XML into a DOM Tree
Recipe 22.3 Parsing XML into SAX Events
Recipe 22.4 Making Simple Changes to Elements or Text
Recipe 22.5 Validating XML
Recipe 22.6 Finding Elements and Text Within an XML Document
Recipe 22.7 Processing XML Stylesheet Transformations
Recipe 22.8 Processing Files Larger Than Available Memory
Recipe 22.9 Reading and Writing RSS Files
Recipe 22.10 Writing XML
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