Effective Awk Programming by Robbins, Arnold -- Read -- Imperial Library of Trantor

Index

Effective awk Programming Dedication Foreword to the Third Edition Foreword to the Fourth Edition Preface

History of awk and gawk A Rose by Any Other Name Using This Book Typographical Conventions

Dark Corners

The GNU Project and This Book How to Stay Current Using Code Examples Safari® Books Online How to Contact Us Acknowledgments

I. The awk Language

1. Getting Started with awk

How to Run awk Programs

One-Shot Throwaway awk Programs Running awk Without Input Files Running Long Programs Executable awk Programs Comments in awk Programs Shell Quoting Issues

Quoting in MS-Windows batch files

Datafiles for the Examples Some Simple Examples An Example with Two Rules A More Complex Example awk Statements Versus Lines Other Features of awk When to Use awk Summary

2. Running awk and gawk

Invoking awk Command-Line Options Other Command-Line Arguments Naming Standard Input The Environment Variables gawk Uses

The AWKPATH Environment Variable The AWKLIBPATH Environment Variable Other Environment Variables

gawk’s Exit Status Including Other Files into Your Program Loading Dynamic Extensions into Your Program Obsolete Options and/or Features Undocumented Options and Features Summary

3. Regular Expressions

How to Use Regular Expressions Escape Sequences Regular Expression Operators Using Bracket Expressions How Much Text Matches? Using Dynamic Regexps gawk-Specific Regexp Operators Case Sensitivity in Matching Summary

4. Reading Input Files

How Input Is Split into Records

Record Splitting with Standard awk Record Splitting with gawk

Examining Fields Nonconstant Field Numbers Changing the Contents of a Field Specifying How Fields Are Separated

Whitespace Normally Separates Fields Using Regular Expressions to Separate Fields Making Each Character a Separate Field Setting FS from the Command Line Making the Full Line Be a Single Field Field-Splitting Summary

Reading Fixed-Width Data Defining Fields by Content Multiple-Line Records Explicit Input with getline

Using getline with No Arguments Using getline into a Variable Using getline from a File Using getline into a Variable from a File Using getline from a Pipe Using getline into a Variable from a Pipe Using getline from a Coprocess Using getline into a Variable from a Coprocess Points to Remember About getline Summary of getline Variants

Reading Input with a Timeout Directories on the Command Line Summary

5. Printing Output

The print Statement print Statement Examples Output Separators Controlling Numeric Output with print Using printf Statements for Fancier Printing

Introduction to the printf Statement Format-Control Letters Modifiers for printf Formats Examples Using printf

Redirecting Output of print and printf Special Files for Standard Preopened Data Streams Special Filenames in gawk

Accessing Other Open Files with gawk Special Files for Network Communications Special Filename Caveats

Closing Input and Output Redirections Summary

6. Expressions

Constants, Variables, and Conversions

Constant Expressions

Numeric and string constants Octal and hexadecimal numbers Regular expression constants

Using Regular Expression Constants Variables

Using variables in a program Assigning variables on the command line

Conversion of Strings and Numbers

How awk converts between strings and numbers Locales can influence conversion

Operators: Doing Something with Values

Arithmetic Operators String Concatenation Assignment Expressions Increment and Decrement Operators

Truth Values and Conditions

True and False in awk Variable Typing and Comparison Expressions

String type versus numeric type Comparison operators String comparison with POSIX rules

Boolean Expressions Conditional Expressions

Function Calls Operator Precedence (How Operators Nest) Where You Are Makes a Difference Summary

7. Patterns, Actions, and Variables

Pattern Elements

Regular Expressions as Patterns Expressions as Patterns Specifying Record Ranges with Patterns The BEGIN and END Special Patterns

Startup and cleanup actions Input/output from BEGIN and END rules

The BEGINFILE and ENDFILE Special Patterns The Empty Pattern

Using Shell Variables in Programs Actions Control Statements in Actions

The if-else Statement The while Statement The do-while Statement The for Statement The switch Statement The break Statement The continue Statement The next Statement The nextfile Statement The exit Statement

Predefined Variables

Built-in Variables That Control awk Built-in Variables That Convey Information Using ARGC and ARGV

Summary

8. Arrays in awk

The Basics of Arrays

Introduction to Arrays Referring to an Array Element Assigning Array Elements Basic Array Example Scanning All Elements of an Array Using Predefined Array Scanning Orders with gawk

Using Numbers to Subscript Arrays Using Uninitialized Variables as Subscripts The delete Statement Multidimensional Arrays

Scanning Multidimensional Arrays

Arrays of Arrays Summary

9. Functions

Built-in Functions

Calling Built-in Functions Numeric Functions String-Manipulation Functions

More about ‘\’ and ‘&’ with sub(), gsub(), and gensub()

Input/Output Functions Time Functions Bit-Manipulation Functions Getting Type Information String-Translation Functions

User-Defined Functions

Function Definition Syntax Function Definition Examples Calling User-Defined Functions

Writing a function call Controlling variable scope Passing function arguments by value or by reference

The return Statement Functions and Their Effects on Variable Typing

Indirect Function Calls Summary

II. Problem Solving with awk

10. A Library of awk Functions

Naming Library Function Global Variables General Programming

Converting Strings to Numbers Assertions Rounding Numbers The Cliff Random Number Generator Translating Between Characters and Numbers Merging an Array into a String Managing the Time of Day Reading a Whole File at Once Quoting Strings to Pass to the Shell

Datafile Management

Noting Datafile Boundaries Rereading the Current File Checking for Readable Datafiles Checking for Zero-Length Files Treating Assignments as Filenames

Processing Command-Line Options Reading the User Database Reading the Group Database Traversing Arrays of Arrays Summary

11. Practical awk Programs

Running the Example Programs Reinventing Wheels for Fun and Profit

Cutting Out Fields and Columns Searching for Regular Expressions in Files Printing Out User Information Splitting a Large File into Pieces Duplicating Output into Multiple Files Printing Nonduplicated Lines of Text Counting Things

A Grab Bag of awk Programs

Finding Duplicated Words in a Document An Alarm Clock Program Transliterating Characters Printing Mailing Labels Generating Word-Usage Counts Removing Duplicates from Unsorted Text Extracting Programs from Texinfo Source Files A Simple Stream Editor An Easy Way to Use Library Functions Finding Anagrams from a Dictionary And Now for Something Completely Different

Summary

III. Moving Beyond Standard awk with gawk

12. Advanced Features of gawk

Allowing Nondecimal Input Data Controlling Array Traversal and Array Sorting

Controlling Array Traversal Sorting Array Values and Indices with gawk

Two-Way Communications with Another Process Using gawk for Network Programming Profiling Your awk Programs Summary

13. Internationalization with gawk

Internationalization and Localization GNU gettext Internationalizing awk Programs Translating awk Programs

Extracting Marked Strings Rearranging printf Arguments awk Portability Issues

A Simple Internationalization Example gawk Can Speak Your Language Summary

14. Debugging awk Programs

Introduction to the gawk Debugger

Debugging in General Debugging Concepts awk Debugging

Sample gawk Debugging Session

How to Start the Debugger Finding the Bug

Main Debugger Commands

Control of Breakpoints Control of Execution Viewing and Changing Data Working with the Stack Obtaining Information About the Program and the Debugger State Miscellaneous Commands

Readline Support Limitations Summary

15. Arithmetic and Arbitrary-Precision Arithmetic with gawk

A General Description of Computer Arithmetic Other Stuff to Know Arbitrary-Precision Arithmetic Features in gawk Floating-Point Arithmetic: Caveat Emptor!

Floating-Point Arithmetic Is Not Exact

Many numbers cannot be represented exactly Be careful comparing values Errors accumulate

Getting the Accuracy You Need Try a Few Extra Bits of Precision and Rounding Setting the Precision Setting the Rounding Mode

Arbitrary-Precision Integer Arithmetic with gawk Standards Versus Existing Practice Summary

16. Writing Extensions for gawk

Introduction Extension Licensing How It Works at a High Level API Description

Introduction General-Purpose Data Types Memory Allocation Functions and Convenience Macros Constructor Functions Registration Functions

Registering an extension function Registering an exit callback function Registering an extension version string Customized input parsers Customized output wrappers Customized two-way processors

Printing Messages Updating ERRNO Requesting Values Accessing and Updating Parameters Symbol Table Access

Variable access and update by name Variable access and update by cookie Creating and using cached values

Array Manipulation

Array data types Array functions Working with all the elements of an array How to create and populate arrays

API Variables

API version constants and variables Informational variables

Boilerplate Code

How gawk Finds Extensions Example: Some File Functions

Using chdir() and stat() C Code for chdir() and stat() Integrating the Extensions

The Sample Extensions in the gawk Distribution

File-Related Functions Interface to fnmatch() Interface to fork(), wait(), and waitpid() Enabling In-Place File Editing Character and Numeric values: ord() and chr() Reading Directories Reversing Output Two-Way I/O Example Dumping and Restoring an Array Reading an Entire File Extension Time Functions API Tests

The gawkextlib Project Summary

IV. Appendices

A. The Evolution of the awk Language

Major Changes Between V7 and SVR3.1 Changes Between SVR3.1 and SVR4 Changes Between SVR4 and POSIX awk Extensions in Brian Kernighan’s awk Extensions in gawk Not in POSIX awk Common Extensions Summary Regexp Ranges and Locales: A Long Sad Story Major Contributors to gawk Summary

B. Installing gawk

The gawk Distribution

Getting the gawk Distribution Extracting the Distribution Contents of the gawk Distribution

Compiling and Installing gawk on Unix-Like Systems

Compiling gawk for Unix-Like Systems Additional Configuration Options The Configuration Process

Installation on Other Operating Systems

Installation on PC Operating Systems

Compiling gawk for PC operating systems Testing gawk on PC operating systems Using gawk on PC operating systems Using gawk in the Cygwin environment Using gawk in the MSYS environment

Compiling and Installing gawk on Vax/VMS and OpenVMS

Compiling gawk on VMS Compiling gawk dynamic extensions on VMS Installing gawk on VMS Running gawk on VMS The VMS GNV project Some VMS systems have an old version of gawk

Reporting Problems and Bugs Other Freely Available awk Implementations Summary

C. GNU General Public License

Index Colophon Copyright

← Prev
Back
Next →

← Prev
Back
Next →