Table of Contents

Preface

History of awk and gawk
The GNU Project and This Book
Acknowledgements

1. Introduction

1.1 Using This Book

Dark Corners

1.2 Typographical Conventions
1.3 Data Files for the Examples

2. Getting Started with awk

2.1 A Rose By Any Other Name
2.2 How to Run awk Programs

2.2.1 One-shot Throw-away awk Programs
2.2.2 Running awk without Input Files
2.2.3 Running Long Programs
2.2.4 Executable awk Programs
2.2.5 Comments in awk Programs

2.3 A Very Simple Example
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. Useful One Line Programs
4. Regular Expressions

4.1 How to Use Regular Expressions
4.2 Escape Sequences
4.3 Regular Expression Operators
4.4 Additional Regexp Operators Only in gawk
4.5 Case-sensitivity in Matching
4.6 How Much Text Matches?
4.7 Using Dynamic Regexps

5. Reading Input Files

5.1 How Input is Split into Records
5.2 Examining Fields
5.3 Non-constant Field Numbers
5.4 Changing the Contents of a Field
5.5 Specifying How Fields are Separated

5.5.1 The Basics of Field Separating
5.5.2 Using Regular Expressions to Separate Fields
5.5.3 Making Each Character a Separate Field
5.5.4 Setting FS from the Command Line
5.5.5 Field Splitting Summary

5.6 Reading Fixed-width Data
5.7 Multiple-Line Records
5.8 Explicit Input with getline

5.8.1 Introduction to getline
5.8.2 Using getline with No Arguments
5.8.3 Using getline Into a Variable
5.8.4 Using getline from a File
5.8.5 Using getline Into a Variable from a File
5.8.6 Using getline from a Pipe
5.8.7 Using getline Into a Variable from a Pipe
5.8.8 Summary of getline Variants

6. Printing Output

6.1 The print Statement
6.2 Examples of print Statements
6.3 Output Separators
6.4 Controlling Numeric Output with print
6.5 Using printf Statements for Fancier Printing

6.5.1 Introduction to the printf Statement
6.5.2 Format-Control Letters
6.5.3 Modifiers for printf Formats
6.5.4 Examples Using printf

6.6 Redirecting Output of print and printf
6.7 Special File Names in gawk
6.8 Closing Input and Output Files and Pipes

7. Expressions

7.1 Constant Expressions

7.1.1 Numeric and String Constants
7.1.2 Regular Expression Constants

7.2 Using Regular Expression Constants
7.3 Variables

7.3.1 Using Variables in a Program
7.3.2 Assigning Variables on the Command Line

7.4 Conversion of Strings and Numbers
7.5 Arithmetic Operators
7.6 String Concatenation
7.7 Assignment Expressions
7.8 Increment and Decrement Operators
7.9 True and False in awk
7.10 Variable Typing and Comparison Expressions
7.11 Boolean Expressions
7.12 Conditional Expressions
7.13 Function Calls
7.14 Operator Precedence (How Operators Nest)

8. Patterns and Actions

8.1 Pattern Elements

8.1.1 Kinds of Patterns
8.1.2 Regular Expressions as Patterns
8.1.3 Expressions as Patterns
8.1.4 Specifying Record Ranges with Patterns
8.1.5 The BEGIN and END Special Patterns

8.1.5.1 Startup and Cleanup Actions
8.1.5.2 Input/Output from BEGIN and END Rules

8.1.6 The Empty Pattern

8.2 Overview of Actions

9. Control Statements in Actions

9.1 The if-else Statement
9.2 The while Statement
9.3 The do-while Statement
9.4 The for Statement
9.5 The break Statement
9.6 The continue Statement
9.7 The next Statement
9.8 The nextfile Statement
9.9 The exit Statement

10. Built-in Variables

10.1 Built-in Variables that Control awk
10.2 Built-in Variables that Convey Information
10.3 Using ARGC and ARGV

11. Arrays in awk

11.1 Introduction to Arrays
11.2 Referring to an Array Element
11.3 Assigning Array Elements
11.4 Basic Array Example
11.5 Scanning All Elements of an Array
11.6 The delete Statement
11.7 Using Numbers to Subscript Arrays
11.8 Using Uninitialized Variables as Subscripts
11.9 Multi-dimensional Arrays
11.10 Scanning Multi-dimensional Arrays
11.11 Using Array Memory Efficiently

12. Built-in Functions

12.1 Calling Built-in Functions
12.2 Numeric Built-in Functions
12.3 Built-in Functions for String Manipulation
12.4 Built-in Functions for Input/Output
12.5 Functions for Dealing with Time Stamps

13. User-defined Functions

13.1 Function Definition Syntax
13.2 Function Definition Examples
13.3 Calling User-defined Functions
13.4 The return Statement

14. Running awk

14.1 Command Line Options
14.2 Other Command Line Arguments
14.3 The AWKPATH Environment Variable
14.4 Obsolete Options and/or Features
14.5 Undocumented Options and Features
14.6 Known Bugs in gawk

15. A Library of awk Functions

15.1 Simulating gawk-specific Features
15.2 Implementing nextfile as a Function
15.3 Assertions
15.4 Rounding Numbers
15.5 Translating Between Characters and Numbers
15.6 Merging an Array Into a String
15.7 Turning Dates Into Timestamps
15.8 Managing the Time of Day
15.9 Noting Data File Boundaries
15.10 Processing Command Line Options
15.11 Reading the User Database
15.12 Reading the Group Database
15.13 Naming Library Function Global Variables

16. Practical awk Programs

16.1 Re-inventing Wheels for Fun and Profit

16.1.1 Cutting Out Fields and Columns
16.1.2 Searching for Regular Expressions in Files
16.1.3 Printing Out User Information
16.1.4 Splitting a Large File Into Pieces
16.1.5 Duplicating Output Into Multiple Files
16.1.6 Printing Non-duplicated Lines of Text
16.1.7 Counting Things

16.2 A Grab Bag of awk Programs

16.2.1 Finding Duplicated Words in a Document
16.2.2 An Alarm Clock Program
16.2.3 Transliterating Characters
16.2.4 Printing Mailing Labels
16.2.5 Generating Word Usage Counts
16.2.6 Removing Duplicates from Unsorted Text
16.2.7 Extracting Programs from Texinfo Source Files
16.2.8 A Simple Stream Editor
16.2.9 An Easy Way to Use Library Functions

17. The Evolution of the awk Language

17.1 Major Changes between V7 and SVR3.1
17.2 Changes between SVR3.1 and SVR4
17.3 Changes between SVR4 and POSIX awk
17.4 Extensions in the Bell Laboratories awk
17.5 Extensions in gawk Not in POSIX awk

A. gawk Summary

A.1 Command Line Options Summary
A.2 Language Summary
A.3 Variables and Fields

A.3.1 Fields
A.3.2 Built-in Variables
A.3.3 Arrays
A.3.4 Data Types

A.4 Patterns

A.4.1 Pattern Summary
A.4.2 Regular Expressions

A.5 Actions

A.5.1 Operators
A.5.2 Control Statements
A.5.3 I/O Statements
A.5.4 printf Summary
A.5.5 Special File Names
A.5.6 Built-in Functions
A.5.7 Time Functions
A.5.8 String Constants

A.6 User-defined Functions
A.7 Historical Features

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 The Configuration Process

B.3 How to Compile and Install gawk on VMS

B.3.1 Compiling gawk on VMS
B.3.2 Installing gawk on VMS
B.3.3 Running gawk on VMS
B.3.4 Building and Using gawk on VMS POSIX

B.4 MS-DOS and OS/2 Installation and Compilation
B.5 Installing gawk on the Atari ST

B.5.1 Compiling gawk on the Atari ST
B.5.2 Running gawk on the Atari ST

B.6 Installing gawk on an Amiga
B.7 Reporting Problems and Bugs
B.8 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 Probable Future Extensions
C.4 Suggestions for Improvements

D. Glossary
GNU GENERAL PUBLIC LICENSE

Preamble
How to Apply These Terms to Your New Programs

Index