awk

最新推荐文章于 2024-12-12 09:27:56 发布

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最新推荐文章于 2024-12-12 09:27:56 发布

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分类专栏： shell 文章标签： shell output system input cmd

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本文深入探讨了awk程序的主要结构、使用Shell命令的方法、内部使用shell变量、内置变量、数组操作、特殊处理以及正则表达式的应用。重点介绍了awk中的数组、FS与SUBSEP的指定选项、以及如何在实际场景中灵活运用awk进行数据处理。

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1，awk程序的主要结构（awk手册）:

awk程序中主要语法是 Pattern { Actions}, 故常见之awk 程序其型态如下 :

Pattern1 { Actions1 }

Pattern2 { Actions2 }

......

Pattern3 { Actions3 }

2，awk 程序中使用 Shell 命令

方法1，awk output 指令 | "Shell 接受的命令"

echo "3 1 5"|awk'{printf("%d\n%d\n%d\n",$1,$2,$3)|"sort -n"}'

方法2 ， "Shell 接受的命令" | awk input 指令

echo|awk '{ while("ps"|getlineline ) print line }'

方法3，使用system（）

方法4，使用print cmd | “/bin/bash”

3，awk内部使用shell变量(赋值变量要加引号)

方法1 sh_v="shellvariable"；echo |awk '{print awk_v}' awk_v="$sh_v"

方法2 sh_v="shellvariable";echo|awk -v awk_v="$sh_v" '{print awk_v}'

Gawk executes AWK programs in the following order. First, all variable assignments specified via the -v option are performed. Next, gawk compiles the program into an internal form. Then, gawk executes the code in the BEGIN block(s) (if any), and then proceeds toread each file named in the ARGV array. If there are no files named on the command line, gawk reads the standard input. If a filename on the command line has the form var=val it is treated as a variable assignment. The variable var will be assigned the value val. (This happens after any BEGIN block(s) have been run.) Command line variable assignment is most useful for dynamically assigning values to the variables AWK uses to control how input is broken into fields and records. It is also useful for controlling state if multiple passes are needed over a single data file.