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This file documents
awk, a program that you can use to select
particular records in a file and perform operations upon them.
This is Edition 1.0.6 of Effective AWK Programming,
for the 3.0.6 version of the GNU implementation
Preface What this Info file is about; brief history and acknowledgements. 1. Introduction What is the
awklanguage; using this Info file.
2. Getting Started with
A basic introduction to using
awk. How to run an
awkprogram. Command line syntax.
3. Useful One Line Programs Short, sample
4. Regular Expressions All about matching things using regular expressions. 5. Reading Input Files How to read files and manipulate fields. 6. Printing Output How to print using
awk. Describes the
Also describes redirection of output.
7. Expressions Expressions are the basic building blocks of statements. 8. Patterns and Actions Overviews of patterns and actions. 9. Control Statements in Actions The various control statements are described in detail. 10. Built-in Variables 11. Arrays in
The description and use of arrays. Also includes array-oriented control statements. 12. Built-in Functions The built-in functions are summarized here. 13. User-defined Functions User-defined functions are described in detail. 14. Running
How to run
15. A Library of
awkprograms with complete explanations.
17. The Evolution of the
The evolution of the
gawkOptions and Language Summary.
gawkunder various operating systems.
C. Implementation Notes Something about the implementation of
D. Glossary An explanation of some unfamiliar terms. GNU GENERAL PUBLIC LICENSE Your right to copy and distribute
Index Concept and Variable Index.
The history of
The GNU Project and This Book Brief history of the GNU project and this Info file. Acknowledgements 1.1 Using This Book Using this Info file. Includes sample input files that you can use. 1.2 Typographical Conventions 1.3 Data Files for the Examples Sample data files for use in the
awkprograms illustrated in this Info file.
2.1 A Rose By Any Other Name What name to use to find
2.2 How to Run
How to run
gawkprograms; includes command line syntax.
2.2.1 One-shot Throw-away
Running a short throw-away
awkwithout Input Files
Using no input files (input from terminal instead). 2.2.3 Running Long Programs Putting permanent
awkprograms in files.
2.2.5 Comments in
Adding documentation to
2.3 A Very Simple Example A very simple example. 2.4 An Example with Two Rules A less simple one-line example with two rules. 2.5 A More Complex Example A more complex example. 2.6
awkStatements Versus Lines
Subdividing or combining statements into lines. 2.7 Other Features of
2.8 When to Use
When to use
gawkand when to use other things.
4.1 How to Use Regular Expressions 4.2 Escape Sequences How to write non-printing characters. 4.3 Regular Expression Operators 4.4 Additional Regexp Operators Only in
Operators specific to GNU software. 4.5 Case-sensitivity in Matching How to do case-insensitive matching. 4.6 How Much Text Matches? How much text matches. 4.7 Using Dynamic Regexps 5.1 How Input is Split into Records Controlling how data is split into records. 5.2 Examining Fields An introduction to fields. 5.3 Non-constant Field Numbers 5.4 Changing the Contents of a Field 5.5 Specifying How Fields are Separated The field separator and how to change it. 5.5.1 The Basics of Field Separating How fields are split with single characters or simple strings. 5.5.2 Using Regular Expressions to Separate Fields Using regexps as the field separator. 5.5.3 Making Each Character a Separate Field Making each character a separate field. 5.5.4 Setting
FSfrom the Command Line
FSfrom the command line.
5.5.5 Field Splitting Summary Some final points and a summary table. 5.6 Reading Fixed-width Data Reading constant width data. 5.7 Multiple-Line Records Reading multi-line records. 5.8 Explicit Input with
Reading files under explicit program control using the
5.8.1 Introduction to
Introduction to the
getlinewith No Arguments
getlinewith no arguments.
getlineInto a Variable
getlineinto a variable.
getlinefrom a File
getlinefrom a file.
getlineInto a Variable from a File
getlineinto a variable from a file.
getlinefrom a Pipe
getlinefrom a pipe.
getlineInto a Variable from a Pipe
getlineinto a variable from a pipe.
5.8.8 Summary of
6.1 The The 6.2 Examples of Simple examples of 6.3 Output Separators The output separators and how to change them. 6.4 Controlling Numeric Output with Controlling Numeric Output With 6.5 Using
printfStatements for Fancier Printing
6.5.1 Introduction to the
Syntax of the
6.5.2 Format-Control Letters Format-control letters. 6.5.3 Modifiers for
Format-specification modifiers. 6.5.4 Examples Using
Several examples. 6.6 Redirecting Output of
How to redirect output to multiple files and pipes. 6.7 Special File Names in
File name interpretation in
gawkallows access to inherited file
6.8 Closing Input and Output Files and Pipes 7.1 Constant Expressions String, numeric, and regexp constants. 7.1.1 Numeric and String Constants Numeric and string constants. 7.1.2 Regular Expression Constants Regular Expression constants. 7.2 Using Regular Expression Constants When and how to use a regexp constant. 7.3 Variables Variables give names to values for later use. 7.3.1 Using Variables in a Program Using variables in your programs. 7.3.2 Assigning Variables on the Command Line Setting variables on the command line and a summary of command line syntax. This is an advanced method of input. 7.4 Conversion of Strings and Numbers The conversion of strings to numbers and vice versa. 7.5 Arithmetic Operators Arithmetic operations (`+', `-', etc.) 7.6 String Concatenation Concatenating strings. 7.7 Assignment Expressions Changing the value of a variable or a field. 7.8 Increment and Decrement Operators Incrementing the numeric value of a variable. 7.9 True and False in
What is "true" and what is "false". 7.10 Variable Typing and Comparison Expressions How variables acquire types, and how this affects comparison of numbers and strings with
("and") and `!' ("not").
7.11 Boolean Expressions Combining comparison expressions using boolean operators `||' ("or"), `&&'
7.12 Conditional Expressions Conditional expressions select between two subexpressions under control of a third subexpression. 7.13 Function Calls A function call is an expression. 7.14 Operator Precedence (How Operators Nest) How various operators nest. 8.1 Pattern Elements What goes into a pattern. 8.1.1 Kinds of Patterns A list of all kinds of patterns. 8.1.2 Regular Expressions as Patterns Using regexps as patterns. 8.1.3 Expressions as Patterns Any expression can be used as a pattern. 8.1.4 Specifying Record Ranges with Patterns Pairs of patterns specify record ranges. 8.1.5 The
Specifying initialization and cleanup rules. 22.214.171.124 Startup and Cleanup Actions How and why to use BEGIN/END rules. 126.96.36.199 Input/Output from
I/O issues in BEGIN/END rules. 8.1.6 The Empty Pattern The empty pattern, which matches every record. 8.2 Overview of Actions What goes into an action. 9.1 The
Conditionally execute some
Loop until some condition is satisfied. 9.3 The
Do specified action while looping until some condition is satisfied. 9.4 The
Another looping statement, that provides initialization and increment clauses. 9.5 The
Immediately exit the innermost enclosing loop. 9.6 The
Skip to the end of the innermost enclosing loop. 9.7 The
Stop processing the current input record. 9.8 The
Stop processing the current file. 9.9 The
Stop execution of
10.1 Built-in Variables that Control
Built-in variables that you change to control
10.2 Built-in Variables that Convey Information Built-in variables where
awkgives you information.
Ways to use
11.1 Introduction to Arrays 11.2 Referring to an Array Element How to examine one element of an array. 11.3 Assigning Array Elements How to change an element of an array. 11.4 Basic Array Example Basic Example of an Array 11.5 Scanning All Elements of an Array A variation of the
forstatement. It loops through the indices of an array's existing elements.
deletestatement removes an element from an array.
11.7 Using Numbers to Subscript Arrays How to use numbers as subscripts in
11.8 Using Uninitialized Variables as Subscripts Using Uninitialized variables as subscripts. 11.9 Multi-dimensional Arrays Emulating multi-dimensional arrays in
11.10 Scanning Multi-dimensional Arrays Scanning multi-dimensional arrays. 12.1 Calling Built-in Functions How to call built-in functions. 12.2 Numeric Built-in Functions Functions that work with numbers, including
12.3 Built-in Functions for String Manipulation Functions for string manipulation, such as
12.4 Built-in Functions for Input/Output Functions for files and shell commands. 12.5 Functions for Dealing with Time Stamps Functions for dealing with time stamps. 13.1 Function Definition Syntax How to write definitions and what they mean. 13.2 Function Definition Examples An example function definition and what it does. 13.3 Calling User-defined Functions Things to watch out for. 13.4 The
Specifying the value a function returns. 14.1 Command Line Options Command line options and their meanings. 14.2 Other Command Line Arguments Input file names and variable assignments. 14.3 The
Searching directories for
14.4 Obsolete Options and/or Features Obsolete Options and/or features. 14.5 Undocumented Options and Features 14.6 Known Bugs in
What to do if you don't have
nextfileas a Function
Two implementations of a
15.3 Assertions A function for assertions in
15.4 Rounding Numbers A function for rounding if
sprintfdoes not do it correctly.
15.5 Translating Between Characters and Numbers Functions for using characters as numbers and vice versa. 15.6 Merging an Array Into a String A function to join an array into a string. 15.7 Turning Dates Into Timestamps A function to turn a date into a timestamp. 15.8 Managing the Time of Day A function to get formatted times. 15.9 Noting Data File Boundaries A function for handling data file transitions. 15.10 Processing Command Line Options A function for processing command line arguments. 15.11 Reading the User Database Functions for getting user information. 15.12 Reading the Group Database Functions for getting group information. 15.13 Naming Library Function Global Variables How to best name private global variables in library functions. 16.1 Re-inventing Wheels for Fun and Profit Clones of common utilities. 16.1.1 Cutting Out Fields and Columns The
16.1.2 Searching for Regular Expressions in Files The
16.1.3 Printing Out User Information The
16.1.4 Splitting a Large File Into Pieces The
16.1.5 Duplicating Output Into Multiple Files The
16.1.6 Printing Non-duplicated Lines of Text The
16.1.7 Counting Things The
16.2 A Grab Bag of
16.2.1 Finding Duplicated Words in a Document Finding duplicated words in a document. 16.2.2 An Alarm Clock Program An alarm clock. 16.2.3 Transliterating Characters A program similar to the
16.2.4 Printing Mailing Labels Printing mailing labels. 16.2.5 Generating Word Usage Counts A program to produce a word usage count. 16.2.6 Removing Duplicates from Unsorted Text Eliminating duplicate entries from a history file. 16.2.7 Extracting Programs from Texinfo Source Files Pulling out programs from Texinfo source files. 16.2.8 A Simple Stream Editor 16.2.9 An Easy Way to Use Library Functions A wrapper for
awkthat includes files.
17.1 Major Changes between V7 and SVR3.1 The major changes between V7 and System V Release 3.1. 17.2 Changes between SVR3.1 and SVR4 Minor changes between System V Releases 3.1 and 4. 17.3 Changes between SVR4 and POSIX
New features from the POSIX standard. 17.4 Extensions in the Bell Laboratories
New features from the Bell Laboratories version of
17.5 Extensions in
gawkNot in POSIX
The extensions in
gawknot in POSIX
A.1 Command Line Options Summary Recapitulation of the command line. A.2 Language Summary A terse review of the language. A.3 Variables and Fields Variables, fields, and arrays. A.3.1 Fields Input field splitting. A.3.2 Built-in Variables
awk's built-in variables.
A.3.3 Arrays Using arrays. A.3.4 Data Types Values in
awkare numbers or strings.
A.4 Patterns Patterns and Actions, and their component parts. A.4.1 Pattern Summary Quick overview of patterns. A.4.2 Regular Expressions Quick overview of regular expressions. A.5 Actions Quick overview of actions. A.5.1 Operators
A.5.2 Control Statements The control statements. A.5.3 I/O Statements The I/O statements. A.5.4
A summary of
A.5.5 Special File Names Special file names interpreted internally. A.5.6 Built-in Functions Built-in numeric and string functions. A.5.7 Time Functions Built-in time functions. A.5.8 String Constants Escape sequences in strings. A.6 User-defined Functions Defining and calling functions. A.7 Historical Features Some undocumented but supported "features". B.1 The
What is in the
B.1.1 Getting the
How to get the distribution. B.1.2 Extracting the Distribution How to extract the distribution. B.1.3 Contents of the
What is in the distribution. B.2 Compiling and Installing
gawkunder various versions of Unix.
B.2.2 The Configuration Process How it's all supposed to work. B.3 How to Compile and Install
How to compile
How to install
How to run
B.3.4 Building and Using
gawkon VMS POSIX
Alternate instructions for VMS POSIX. B.4 MS-DOS and OS/2 Installation and Compilation Installing and Compiling
gawkon MS-DOS and OS/2
gawkon the Atari ST
gawkon the Atari ST
gawkon the Atari ST
gawkon an Amiga
B.7 Reporting Problems and Bugs B.8 Other Freely Available
Other freely available
C.1 Downward Compatibility and Debugging How to disable certain
C.2 Making Additions to
Making Additions To
C.2.1 Adding New Features Adding code to the main body of
gawkto a New Operating System
gawkto a new operating system.
C.3 Probable Future Extensions New features that may be implemented one day. C.4 Suggestions for Improvements Suggestions for improvements by volunteers.