awk 命令簡介

1. awk 相較於 sed 作用於一整個行的處理，awk 是『以行為一次處理的單位』， 而『以欄位為最小的處理單位』。awk 命令輔助說明如下：

   [dywang@dywmac zzz]$ awk --help
   Usage: awk [POSIX or GNU style options] -f progfile [--] file ...
   Usage: awk [POSIX or GNU style options] [--] 'program' file ...
   POSIX options:		GNU long options:
   	-f progfile		--file=progfile
   	-F fs			--field-separator=fs
   	-v var=val		--assign=var=val
   	-m[fr] val
   	-O			--optimize
   	-W compat		--compat
   	-W copyleft		--copyleft
   	-W copyright		--copyright
   	-W dump-variables[=file]	--dump-variables[=file]
   	-W exec=file		--exec=file
   	-W gen-po		--gen-po
   	-W help			--help
   	-W lint[=fatal]		--lint[=fatal]
   	-W lint-old		--lint-old
   	-W non-decimal-data	--non-decimal-data
   	-W profile[=file]	--profile[=file]
   	-W posix		--posix
   	-W re-interval		--re-interval
   	-W source=program-text	--source=program-text
   	-W traditional		--traditional
   	-W usage		--usage
   	-W use-lc-numeric	--use-lc-numeric
   	-W version		--version
   
   To report bugs, see node `Bugs' in `gawk.info', which is
   section `Reporting Problems and Bugs' in the printed version.
   
   gawk is a pattern scanning and processing language.
   By default it reads standard input and writes standard output.
   
   Examples:
   	gawk '{ sum += $1 }; END { print sum }' file
   	gawk -F: '{ print $1 }' /etc/passwd
   

2. awk --dump-variables dump 所有變數，指定的檔案空字串，則預設存在 awkvars.out，其中 FS: string (" ") 表示欄位分隔符號為空白 " "。

   [dywang@dywmac ~]$ awk --dump-variables ”
   [dywang@dywmac ~]$ cat awkvars.out 
   ARGC: number (1)
   ARGIND: number (0)
   ARGV: array, 1 elements
   BINMODE: number (0)
   CONVFMT: string ("%.6g")
   ERRNO: number (0)
   FIELDWIDTHS: string ("")
   FILENAME: string ("")
   FNR: number (0)
   FS: string (" ")
   IGNORECASE: number (0)
   LINT: number (0)
   NF: number (0)
   NR: number (0)
   OFMT: string ("%.6g")
   OFS: string (" ")
   ORS: string ("\n")
   RLENGTH: number (0)
   RS: string ("\n")
   RSTART: number (0)
   RT: string ("")
   SUBSEP: string ("\034")
   TEXTDOMAIN: string ("messages")
   

3. 查看 awk 命令連結到 gwak，也就是在 Linux 上 awk 是 gawk。

   [dywang@dywmac zzz]$ ll /usr/bin/awk 
   lrwxrwxrwx. 1 root root 14 Jun  2  2018 /usr/bin/awk -> ../../bin/gawk
   

4. gawk --version (GNU Awk) 版本宣告，是自由軟體。

   [dywang@dywmac zzz]$ gawk -W version
   GNU Awk 3.1.7
   Copyright (C) 1989, 1991-2009 Free Software Foundation.
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program. If not, see http://www.gnu.org/licenses/.