Awk基本入门[3] Awk Variables and Operators

1、Variables

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You don't need to declare an variable to use it. If you wish to initialize an awk variable, it is better to do it in the BEGIN section, which will be executed only once.

There are no data types in Awk. Whether an awk variable is a number or a string depends on the context in which the variable is used in.

employee-sal.txt sample file
employee-sal.txt is a comma delimited file that contains 5 employee records in the following format:

$ 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

The following example shows how to create and use your own variable inside an awk script. In this example, "total" is the user defined Awk variable that is used to calculate the total salary of all the employees in the company.

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

2、 Operators

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Unary Operators

An operator which accepts a single operand is called a unary operator.

Unary Operators

Operator	Description
+	The number (returns the number itself)
-	Negate the number
++	Auto Increment
--	Auto Decrement

Arithmetic Operators

An operator that accepts two operands is called a binary operator.

Arithmetric  Operator

Operator	Description
+	Addtion
-	Subtraction
*	Multiplication
/	Devision
%	Module Devision

String Operator

(space) is a string operator that does string concatenation.

$ cat string.awk
BEGIN {
FS=",";
OFS=",";
string1="Audio";
string2="Video";
numberstring="100";
string3=string1 string2;
print "Concatenate string is:" string3;
numberstring=numberstring+1;
print "String to number:" numberstring;
}
$ awk -f string.awk items.txt
Concatenate string is:AudioVideo
String to number:101

Assignment Operators

Comparison Operators 

Operator	Description
>	Is greater than
>=	Is greater than or equal to
<	Is less than
<=	Is less than or equal to
==	Is equal to
!=	Is not　equal to
&&	Both the conditional expressions are true
||	Either one of the conditional expressions is true

3、Regular Expression Operators

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Print lines where field two contains “Tennis”:

$ awk -F "," '$2 ~ "Tennis"' items.txt
104,Tennis Racket,Sports,190,20

Print lines where field two does not contain “Tennis”:

$ awk -F "," '$2 !~ "Tennis"' items.txt
101,HD Camcorder,Video,210,10
102,Refrigerator,Appliance,850,2
103,MP3 Player,Audio,270,15
105,Laser Printer,Office,475,5