Table of Contents

Foreword
Preface

History of awk and gawk
1.0 A Rose by Any Other Name
1.1 Using This Book
1.2 Typographical Conventions
The GNU Project and This Book
How to Contribute
Acknowledgments

2. Getting Started with awk

2.1 How to Run awk Programs

2.1.1 One-Shot Throw-Away awk Programs
2.1.2 Running awk Without Input Files
2.1.3 Running Long Programs
2.1.4 Executable awk Programs
2.1.5 Comments in awk Programs
2.1.6 Shell Quoting Issues

2.2 Data Files for the Examples
2.3 Some Simple Examples
2.4 An Example with Two Rules
2.5 A More Complex Example
2.6 awk Statements Versus Lines
2.7 Other Features of awk
2.8 When to Use awk

3. Regular Expressions

3.1 How to Use Regular Expressions
3.2 Escape Sequences
3.3 Regular Expression Operators
3.4 Using Character Lists
3.5 gawk-Specific Regexp Operators
3.6 Case Sensitivity in Matching
3.7 How Much Text Matches?
3.8 Using Dynamic Regexps

4. Reading Input Files

4.1 How Input Is Split into Records
4.2 Examining Fields
4.3 Non-Constant Field Numbers
4.4 Changing the Contents of a Field
4.5 Specifying How Fields Are Separated

4.5.1 Using Regular Expressions to Separate Fields
4.5.2 Making Each Character a Separate Field
4.5.3 Setting FS from the Command Line
4.5.4 Field Splitting Summary

4.6 Reading Fixed-Width Data
4.7 Multiple-Line Records
4.8 Explicit Input with getline

4.8.1 Using getline with No Arguments
4.8.2 Using getline into a Variable
4.8.3 Using getline from a File
4.8.4 Using getline into a Variable from a File
4.8.5 Using getline from a Pipe
4.8.6 Using getline into a Variable from a Pipe
4.8.7 Using getline from a Coprocess
4.8.8 Using getline into a Variable from a Coprocess
4.8.9 Points About getline to Remember
4.8.10 Summary of getline Variants

5. Printing Output

5.1 The print Statement
5.2 Examples of print Statements
5.3 Output Separators
5.4 Controlling Numeric Output with print
5.5 Using printf Statements for Fancier Printing

5.5.1 Introduction to the printf Statement
5.5.2 Format-Control Letters
5.5.3 Modifiers for printf Formats
5.5.4 Examples Using printf

5.6 Redirecting Output of print and printf
5.7 Special File Names in gawk

5.7.1 Special Files for Standard Descriptors
5.7.2 Special Files for Process-Related Information
5.7.3 Special Files for Network Communications
5.7.4 Special File Name Caveats

5.8 Closing Input and Output Redirections

6. Expressions

6.1 Constant Expressions

6.1.1 Numeric and String Constants
6.1.2 Octal and Hexadecimal Numbers
6.1.3 Regular Expression Constants

6.2 Using Regular Expression Constants
6.3 Variables

6.3.1 Using Variables in a Program
6.3.2 Assigning Variables on the Command Line

6.4 Conversion of Strings and Numbers
6.5 Arithmetic Operators
6.6 String Concatenation
6.7 Assignment Expressions
6.8 Increment and Decrement Operators
6.9 True and False in awk
6.10 Variable Typing and Comparison Expressions
6.11 Boolean Expressions
6.12 Conditional Expressions
6.13 Function Calls
6.14 Operator Precedence (How Operators Nest)

7. Patterns, Actions, and Variables

7.1 Pattern Elements

7.1.1 Regular Expressions as Patterns
7.1.2 Expressions as Patterns
7.1.3 Specifying Record Ranges with Patterns
7.1.4 The BEGIN and END Special Patterns

7.1.4.1 Startup and Cleanup Actions
7.1.4.2 Input/Output from BEGIN and END Rules

7.1.5 The Empty Pattern

7.2 Using Shell Variables in Programs
7.3 Actions
7.4 Control Statements in Actions

7.4.1 The if-else Statement
7.4.2 The while Statement
7.4.3 The do-while Statement
7.4.4 The for Statement
7.4.5 The break Statement
7.4.6 The continue Statement
7.4.7 The next Statement
7.4.8 Using gawk's nextfile Statement
7.4.9 The exit Statement

7.5 Built-in Variables

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

8. Arrays in awk

8.1 Introduction to Arrays
8.2 Referring to an Array Element
8.3 Assigning Array Elements
8.4 Basic Array Example
8.5 Scanning All Elements of an Array
8.6 The delete Statement
8.7 Using Numbers to Subscript Arrays
8.8 Using Uninitialized Variables as Subscripts
8.9 Multidimensional Arrays
8.10 Scanning Multidimensional Arrays
8.11 Sorting Array Values and Indices with gawk

9. Functions

9.1 Built-in Functions

9.1.1 Calling Built-in Functions
9.1.2 Numeric Functions
9.1.3 String Manipulation Functions

9.1.3.1 More About `\' and `&' with sub, gsub, and gensub

9.1.4 Input/Output Functions
9.1.5 Using gawk's Timestamp Functions
9.1.6 Using gawk's Bit Manipulation Functions
9.1.7 Using gawk's String Translation Functions

9.2 User-Defined Functions

9.2.1 Function Definition Syntax
9.2.2 Function Definition Examples
9.2.3 Calling User-Defined Functions
9.2.4 The return Statement
9.2.5 Functions and Their Effect on Variable Typing

10. Internationalization with gawk

10.1 Internationalization and Localization
10.2 GNU gettext
10.3 Internationalizing awk Programs
10.4 Translating awk Programs

10.4.1 Extracting Marked Strings
10.4.2 Rearranging printf Arguments
10.4.3 awk Portability Issues

10.5 A Simple Internationalization Example
10.6 gawk Can Speak Your Language

11. Advanced Features of gawk

11.1 Allowing Non-Decimal Input Data
11.2 Two-Way Communications with Another Process
11.3 Using gawk for Network Programming
11.4 Using gawk with BSD Portals
11.5 Profiling Your awk Programs

12. Running awk and gawk

12.1 Invoking awk
12.2 Command-Line Options
12.3 Other Command-Line Arguments
12.4 The AWKPATH Environment Variable
12.5 Obsolete Options and/or Features
12.6 Undocumented Options and Features
12.7 Known Bugs in gawk

13. A Library of awk Functions

13.1 Naming Library Function Global Variables
13.2 General Programming

13.2.1 Implementing nextfile as a Function
13.2.2 Assertions
13.2.3 Rounding Numbers
13.2.4 The Cliff Random Number Generator
13.2.5 Translating Between Characters and Numbers
13.2.6 Merging an Array into a String
13.2.7 Managing the Time of Day

13.3 Data File Management

13.3.1 Noting Data File Boundaries
13.3.2 Rereading the Current File
13.3.3 Checking for Readable Data Files
13.3.4 Treating Assignments as File Names

13.4 Processing Command-Line Options
13.5 Reading the User Database
13.6 Reading the Group Database

14. Practical awk Programs

14.1 Running the Example Programs
14.2 Reinventing Wheels for Fun and Profit

14.2.1 Cutting out Fields and Columns
14.2.2 Searching for Regular Expressions in Files
14.2.3 Printing out User Information
14.2.4 Splitting a Large File into Pieces
14.2.5 Duplicating Output into Multiple Files
14.2.6 Printing Non-Duplicated Lines of Text
14.2.7 Counting Things

14.3 A Grab Bag of awk Programs

14.3.1 Finding Duplicated Words in a Document
14.3.2 An Alarm Clock Program
14.3.3 Transliterating Characters
14.3.4 Printing Mailing Labels
14.3.5 Generating Word Usage Counts
14.3.6 Removing Duplicates from Unsorted Text
14.3.7 Extracting Programs from Texinfo Source Files
14.3.8 A Simple Stream Editor
14.3.9 An Easy Way to Use Library Functions

A. The Evolution of the awk Language

A.1 Major Changes Between V7 and SVR3.1
A.2 Changes Between SVR3.1 and SVR4
A.3 Changes Between SVR4 and POSIX awk
A.4 Extensions in the Bell Laboratories awk
A.5 Extensions in gawk Not in POSIX awk
A.6 Major Contributors to gawk

B. Installing gawk

B.1 The gawk Distribution

B.1.1 Getting the gawk Distribution
B.1.2 Extracting the Distribution
B.1.3 Contents of the gawk Distribution

B.2 Compiling and Installing gawk on Unix

B.2.1 Compiling gawk for Unix
B.2.2 Additional Configuration Options
B.2.3 The Configuration Process

B.3 Installation on Other Operating Systems

B.3.1 Installing gawk on an Amiga
B.3.2 Installing gawk on BeOS
B.3.3 Installation on PC Operating Systems

B.3.3.1 Installing a Prepared Distribution for PC Systems
B.3.3.2 Compiling gawk for PC Operating Systems
B.3.3.3 Using gawk on PC Operating Systems

B.3.4 How to Compile and Install gawk on VMS

B.3.4.1 Compiling gawk on VMS
B.3.4.2 Installing gawk on VMS
B.3.4.3 Running gawk on VMS
B.3.4.4 Building and Using gawk on VMS POSIX

B.4 Unsupported Operating System Ports

B.4.1 Installing gawk on the Atari ST

B.4.1.1 Compiling gawk on the Atari ST
B.4.1.2 Running gawk on the Atari ST

B.4.2 Installing gawk on a Tandem

B.5 Reporting Problems and Bugs
B.6 Other Freely Available awk Implementations

C. Implementation Notes

C.1 Downward Compatibility and Debugging
C.2 Making Additions to gawk

C.2.1 Adding New Features
C.2.2 Porting gawk to a New Operating System

C.3 Adding New Built-in Functions to gawk

C.3.1 A Minimal Introduction to gawk Internals
C.3.2 Directory and File Operation Built-ins

C.3.2.1 Using chdir and stat
C.3.2.2 C Code for chdir and stat
C.3.2.3 Integrating the Extensions

C.4 Probable Future Extensions

D. Basic Programming Concepts

D.1 What a Program Does
D.2 Data Values in a Computer
D.3 Floating-Point Number Caveats

Glossary
GNU General Public License

Preamble
Terms and Conditions for Copying, Distribution and Modification
How to Apply These Terms to Your New Programs

GNU Free Documentation License

ADDENDUM: How to use this License for your documents

Index