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Chapter 12. The gawk Pattern Processing LanguageIN THIS CHAPTER Syntax 528 Arguments 528 Options 529 Patterns 530 Actions 531 Variables 531 Functions 532 Associative Arrays 534 Control Structures 535 Examples 537 getline: Controlling Input 554 Coprocess: Two-Way I/O 557 Getting Input from a Network 558 Error Messages 559 The gawk (GNU 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 gawk language is data driven: You describe the data you want to work with and tell gawk what to do with the data once it finds it. You can use gawk to generate reports or filter text. It works equally well with numbers and text; when you mix the two, gawk usually comes up with the right answer. The authors of awk (Alfred V. Aho, Peter J. Weinberger, and Brian W. Kernighan), on which gawk is based, designed the original utility to be easy to use. To achieve this end they sacrificed execution speed. The gawk utility takes many of its constructs from the C programming language. It includes the following features:
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