Originally developed by Alfred Aho, Brian Kernighan, and Peter Weinberger in 1977, AWK is a pattern-matching language for writing short programs to perform common data-manipulation tasks.

Computer users spend a lot of time doing simple mechanical data manipulation -- changing the format of data, checking its validity, finding items with some property, adding up numbers, printing reports, and the like. All of these jobs ought to be mechanized, but it's a real nuisance to have to write a special-purpose program in a standard language like C or Pascal each time such a task comes up.Awk is a programming language that makes it possible to handle such tasks with very short programs, often only one or two lines long. An awk program is a sequence of patterns and actions that tell what to look for in the input data and what to do when it's found. Awk searches a set of files for lines matched by any of the patterns; when a matching line is found, the corresponding action is performed. A pattern can select lines by combinations of regular expressions and comparison operations on strings, numbers, fields, variables, and array elements. Actions may perform arbutrary processing on selected lines,; the action language looks like C but there are no declarations, and strings and numbers are built-in data types.Awk scans the input files and splits each input line into fields automatically. Because so many things are automatic--input, field splitting, storage management, initialization--awk programs are usually much smaller than they would be in a more conventional language. Thus one common use of awk is for the kind of data manipulation suggested above. Programs, a line or two long, are composed at the keyboard, run once, then discarded. In effect, awk is a general-purpose programable tool that can replace a host of specialized tools or programs.The same brevity of expression and convenience of operations make awk valuable for prototyping larger programs. One starts with a few lines, then refines the program unitil it doesth edesired job, experimenting with designs by trying alternatives quickly. Since programs are short, it's easy to get started, and easy to start over when experience suggests a different direction. And, it's straightforward to translate an awk program into another language once the design is right. Organization of the BookThe first goal of this book is to teach you what awk is and how to use it effectively. Chapter 1 is a tutorial on the bare minimum necessary to get started; after reading even a few pages you should have enough information to begin writing useful programs. The examples in this chapter are very short and simple, typical othe interactive use of awk.Chapter 2 covers the entire language in a systematic order. Although there are plenty of examples in this chapter, like most manuals it's long and a bit dry, so you will probably want to skim it on a first reading.The rest of the book contains a wide variety of examples, chosen to show the breadth of applicability of awk and how to make good use of its facilities. Some of the programs are in regular use in our environment; others show ideas but are not intended for production use; a few are included just because they are fun.The emphasis in Chapter 3 is on retrieval, transformation, reduction and validation of data--the tasks that awk was originally designed for. There is also a discussion of how to handle data like address lists that naturally comes in multiline chunks.Awk is a good language for managing small, personal databases. Chapter 4 discusses the generation of reports from databases, and builds a simple relational database system and query language for data stored in multiple files.Awk handles text with much the same convenience that most languages handle numbers, so it often finds application in text processing. Chapter 5 describes programs for generating text, and some that help with document preparation. One of the examples is an indexing program based on the one we used for this book.Chapter