|
AWK is an interpreted programming language designed for text processing and typically used as a data extraction and reporting tool. It is a standard feature of most Unix-like operating systems. The AWK language is a data-driven scripting language consisting of a set of actions to be taken against streams of textual data – either run directly on files or used as part of a pipeline – for purposes of extracting or transforming text, such as producing formatted reports. The language extensively uses the string datatype, associative arrays (that is, arrays indexed by key strings), and regular expressions. While AWK has a limited intended application domain and was especially designed to support one-liner programs, the language is Turing-complete, and even the early Bell Labs users of AWK often wrote well-structured large AWK programs. AWK was created at Bell Labs in the 1970s,〔(Awk -- A Pattern Scanning and Processing Language (Second Edition) (1978) )〕 and its name is derived from the family names of its authors – Alfred Aho, Peter Weinberger, and Brian Kernighan. The acronym is pronounced the same as the name of the bird auk (which acts as an emblem of the language such as on (The AWK Programming Language ) book cover – the book is often referred to by the abbreviation ''TAPL''). When written in all lowercase letters, as awk, it refers to the Unix or Plan 9 program that runs scripts written in the AWK programming language.==History== AWK was initially developed in 1977 by Alfred Aho, Peter Weinberger, and Brian Kernighan, from whose initials the language takes it name. As one of the early tools to appear in Version 7 Unix, AWK added computational features to a Unix pipeline besides the Bourne shell, the only scripting language available in a standard Unix environment. It is one of the mandatory utilities of the Single UNIX Specification,〔(The Single UNIX Specification, Version 3, Utilities Interface Table )〕 and is required by the Linux Standard Base specification.〔(Linux Standard Base Core Specification 4.0, Chapter 15. Commands and Utilities )〕 AWK was significantly revised and expanded in 1985–88, resulting in the GNU AWK implementation written by Paul Rubin, Jay Fenlason, and Richard Stallman, released in 1988.〔 GNU AWK is the most widely deployed version because it is included with GNU-based Linux packages. GNU AWK has been maintained solely by Arnold Robbins since 1994. Brian Kernighan's nawk (New AWK) source was first released in 1993 unpublicized, and publicly since the late 1990s; many BSD systems use it to avoid GPL license.〔 AWK was preceded by sed (1974). Both were designed for text processing. They share the line-oriented, data-driven paradigm, and are particularly suited to writing one-liner programs, due to the implicit main loop and current line variables. The power and terseness of early AWK programs – notably the powerful regular expression handling and conciseness due to implicit variables, which facilitate one-liners – together with the limitations of AWK at the time, were important inspirations for the Perl language (1987). In the 1990s, Perl became very popular, competing with AWK in the niche of Unix text-processing languages. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「AWK」の詳細全文を読む スポンサード リンク
|