Chapter 2. Numbers :: Perl tutorial :: Programming

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Chapter: Chapter 2. Numbers

Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin.
John von Neumann (1951)

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Perl tutorial

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

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Chapter: Chapter 2. Numbers