The AWK Programming Language

Resource: https://github.com/wuzhouhui/awk

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.

• Patterns can select lines by combinations of regular expressions and comparison operations on strings, numbers, fields, variables, and array elements.

• Actions may perform arbitrary 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 programmable tool that can replace a host of specialized tools or programs.