Chapter 14. The awk Pattern Processing Language

Chapter 14. The awk Pattern Processing Language

IN THIS CHAPTER

Syntax	610
Arguments	610
Options	611
Patterns	612
Actions	612
Variables	613
Functions	614
Associative Arrays	615
Control Structures	616
Examples	618
getline: Controlling Input	634
Error Messages	637

The awk utility is a pattern-scanning and processing language that searches one or more files to see whether they contain records (usually lines) that match specified patterns. It processes lines by performing actions, such as writing the record to standard output or incrementing a counter, each time it finds a match. As opposed to procedural languages, the awk language is data driven: You describe the data you want to work with and tell awk what to do with the data once it finds it.

You can use awk to generate reports or filter text. It works equally well with numbers and text; when you mix the two, awk usually comes up with the right answer. The authors of awk (Alfred V. Aho, Peter J. Weinberger, and Brian W. Kernighan) designed the original utility to be easy to use. To achieve this end they sacrificed execution speed.

The awk utility takes many of its constructs from the C programming language. It includes the following features:

• Flexible format

• Conditional execution

• Looping statements

• Numeric variables

• String variables

• Regular expressions

• Relational expressions

• C's printf