gawk

AWK Language Programming

A User's Guide for GNU AWK

Edition 1.0

January 1996

• Preface
  • History of awk and gawk
  • The GNU Project and This Book
  • Acknowledgements
• Introduction
  • Using This Book
    • Dark Corners
  • Typographical Conventions
  • Data Files for the Examples
• Getting Started with awk
  • A Rose By Any Other Name
  • How to Run awk Programs
    • One-shot Throw-away awk Programs
    • Running awk without Input Files
    • Running Long Programs
    • Executable awk Programs
    • Comments in awk Programs
  • A Very Simple Example
  • An Example with Two Rules
  • A More Complex Example
  • awk Statements Versus Lines
  • Other Features of awk
  • When to Use awk
• Useful One Line Programs
• Regular Expressions
  • How to Use Regular Expressions
  • Escape Sequences
  • Regular Expression Operators
  • Additional Regexp Operators Only in gawk
  • Case-sensitivity in Matching
  • How Much Text Matches?
  • Using Dynamic Regexps
• Reading Input Files
  • How Input is Split into Records
  • Examining Fields
  • Non-constant Field Numbers
  • Changing the Contents of a Field
  • Specifying How Fields are Separated
    • The Basics of Field Separating
    • Using Regular Expressions to Separate Fields
    • Making Each Character a Separate Field
    • Setting FS from the Command Line
    • Field Splitting Summary
  • Reading Fixed-width Data
  • Multiple-Line Records
  • Explicit Input with getline
    • Introduction to 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
    • Summary of getline Variants
• Printing Output
  • The print Statement
  • Examples of print Statements
  • 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 File Names in gawk
  • Closing Input and Output Files and Pipes
• Expressions
  • Constant Expressions
    • Numeric and String Constants
    • Regular Expression Constants
  • Using Regular Expression Constants
  • Variables
    • Using Variables in a Program
    • Assigning Variables on the Command Line
  • Conversion of Strings and Numbers
  • Arithmetic Operators
  • String Concatenation
  • Assignment Expressions
  • Increment and Decrement Operators
  • True and False in awk
  • Variable Typing and Comparison Expressions
  • Boolean Expressions
  • Conditional Expressions
  • Function Calls
  • Operator Precedence (How Operators Nest)
• Patterns and Actions
  • Pattern Elements
    • Kinds of Patterns
    • 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 Empty Pattern
  • Overview of Actions
• Control Statements in Actions
  • The if-else Statement
  • The while Statement
  • The do-while Statement
  • The for Statement
  • The break Statement
  • The continue Statement
  • The next Statement
  • The nextfile Statement
  • The exit Statement
• Built-in Variables
  • Built-in Variables that Control awk
  • Built-in Variables that Convey Information
  • Using ARGC and ARGV
• Arrays in awk
  • Introduction to Arrays
  • Referring to an Array Element
  • Assigning Array Elements
  • Basic Array Example
  • Scanning All Elements of an Array
  • The delete Statement
  • Using Numbers to Subscript Arrays
  • Using Uninitialized Variables as Subscripts
  • Multi-dimensional Arrays
  • Scanning Multi-dimensional Arrays
• Built-in Functions
  • Calling Built-in Functions
  • Numeric Built-in Functions
  • Built-in Functions for String Manipulation
  • Built-in Functions for Input/Output
  • Functions for Dealing with Time Stamps
• User-defined Functions
  • Function Definition Syntax
  • Function Definition Examples
  • Calling User-defined Functions
  • The return Statement
• Running awk
  • Command Line Options
  • Other Command Line Arguments
  • The AWKPATH Environment Variable
  • Obsolete Options and/or Features
  • Undocumented Options and Features
  • Known Bugs in gawk
• A Library of awk Functions
  • Simulating gawk-specific Features
  • Implementing nextfile as a Function
  • Assertions
  • Translating Between Characters and Numbers
  • Merging an Array Into a String
  • Turning Dates Into Timestamps
  • Managing the Time of Day
  • Noting Data File Boundaries
  • Processing Command Line Options
  • Reading the User Database
  • Reading the Group Database
  • Naming Library Function Global Variables
• Practical awk Programs
  • Re-inventing 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 Non-duplicated 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
• 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 the AT&T Bell Laboratories awk
  • Extensions in gawk Not in POSIX awk
• gawk Summary
  • Command Line Options Summary
  • Language Summary
  • Variables and Fields
    • Fields
    • Built-in Variables
    • Arrays
    • Data Types
  • Patterns
    • Pattern Summary
    • Regular Expressions
  • Actions
    • Operators
    • Control Statements
    • I/O Statements
    • printf Summary
    • Special File Names
    • Built-in Functions
    • Time Functions
    • String Constants
  • User-defined Functions
  • Historical Features
• Installing gawk
  • The gawk Distribution
    • Getting the gawk Distribution
    • Extracting the Distribution
    • Contents of the gawk Distribution
  • Compiling and Installing gawk on Unix
    • Compiling gawk for Unix
    • The Configuration Process
  • How to Compile and Install gawk on VMS
    • Compiling gawk on VMS
    • Installing gawk on VMS
    • Running gawk on VMS
    • Building and Using gawk on VMS POSIX
  • MS-DOS and OS/2 Installation and Compilation
  • Installing gawk on the Atari ST
    • Compiling gawk on the Atari ST
    • Running gawk on the Atari ST
  • Installing gawk on an Amiga
  • Reporting Problems and Bugs
  • Other Freely Available awk Implementations
• Implementation Notes
  • Downward Compatibility and Debugging
  • Making Additions to gawk
    • Adding New Features
    • Porting gawk to a New Operating System
  • Probable Future Extensions
  • Suggestions for Improvements
• Glossary
• GNU GENERAL PUBLIC LICENSE
  • Preamble
  • TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
  • How to Apply These Terms to Your New Programs
• Index