[Shell] Bash variables: numeric operations and operators

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The types of variables in the shell are all strings by default, so:

#!/bin/Bashaa=1bb=2cc= $aa +$bbEcho $cc        1+2

Number of ways to calculate:

Declare declares the type of the variable:

　　　　declare [+/-] [option] Variable name

Options:

-: Set type attribute to variable

+: Cancels the Type property of a variable

-I: Declaring a variable as an integer (int)

-x: Declaring a variable as an environment variable

-P: Displays the declared type of the specified variable

Aa=1bb=2cc= $aa +-P AA    # DECLARE--aa="1" -P AA # Declare-x Aa= "1", declare has a-CC =       $aa +$BB  # declare cc as numeric   echo $cc         3

Method 1 (DECLARE):

　　Declare-i cc= $aa + $bb

Method 2 (expr or let numeric arithmetic tool):

　　dd=$ (expr $aa + $bb) # dd value is AA and BB and the + number must have a space on both sides to be valid

Method 3:

　　$ (expression) or $[expression] # If you use a single parenthesis, it means that the system command is included

Operators are: Assignment operators, numeric operators, logical operators.

echo $ ((aa=1)) # 1

echo $ ((6%4)) # 6

echo $ ((1 && 0)) # 0

Link:http://www.cnblogs.com/farwish/p/4772110.html

@ Black eyed poet <www.farwish.com>

[Shell] Bash variables: numeric operations and operators