Chapter 10. Awk Variables and Operators

62. Variables(变量)

关键字不能被使用为变量名。
和其他的编程语言不同，你不需要声明变量才能使用它。
如果你想初始化变量，最好在BEGIN块，它将只执行一次

实例

创建一个文件

$ vi employee-sal.txt

101,John Doe,CEO,10000
102,Jason Smith,IT Manager,5000
103,Raj Reddy,Sysadmin,4500
104,Anand Ram,Developer,4500
105,Jane Miller,Sales Manager,3000

编写一个awk脚本,统计薪水

$ cat total-company-salary.awk
BEGIN {
	FS=",";
	total=0;
}
{
	print $2 "'s salary is: " $4;
	total=total+$4
} END {
	print "---\nTotal company salary = $"total;
}

$ awk -f total-company-salary.awk employee-sal.txt
John Doe's salary is: 10000
Jason Smith's salary is: 5000
Raj Reddy's salary is: 4500
Anand Ram's salary is: 4500
Jane Miller's salary is: 3000
---
Total company salary = $27000

63. Unary Operators（单元操作符）

和数字前的正负号和C语言的自加自减符号一样
遵循负负得正原则

$ vi negative.txt
-1
-2
-3

$ awk '{print +$1}' negative.txt
-1
-2
-3

$ awk '{print -$1}' negative.txt
1
2
3

awk '{print ++$1}' negative.txt 
0
-1
-2

awk '{print $1++,$1}' negative.txt 
-1 0
-2 -1
-3 -2

64. Arithmetic Operators(算数运算符)

65. String Operator(字符串运算符)

空格`是字符串操作符，链接两个字符串string3=string1 string2`

66. Assignment Operators(赋值运算符)

like C
=、+=、-=、*=、/=、%=

67. Comparison Operators(对比运算符)

like C
>、>=、<、<=、!=、==、&&、||

68. Regular Expression Operators(正则表达式运算符)

• ~ 匹配正则表达式
• !~ 不匹配正则表达式(匹配不符合的)