Five, Shell operations

Integer numeric Operations

use the expr command: You can only do integer operations and return the calculation results by default

Format:

Expr integer 1 operator integer 2 ...

Integer values can be supplied with variables, giving the result of the operation directly

+    addition   expr 43 + 21, expr $X + $Y-    subtraction expr 43-21, expr $X-$Y\*       multiplication C8>EXPR 43 \* 21, expr $X \* $Y/        Division expr 43/21, expr $X/$Y% ofthe       remainder expr 43 % 21, expr $X% $Y　

Example:

#!/bin/" Please enter the first number "" Please enter the second number  " num2sum = ' expr $num 1 +  '$num 1 + $num 2 = $sum"

use $[] or $ (()) Expressions

With echo output, the type of operation is analogous to expr multiplication * without the escape character when using a variable, specify the variable name directly without adding the $ symbol

How to perform arithmetic operations in the shell:

Let arithmetic expression let   c= $A +$B $[arithmetic expression]    C =$[$A +$B]$ ((arithmetic expression))    C=$ (($A +  $B)) expr arithmetic operation expression,
There should be a space between the operands and operators in the expression.
and to use a command to reference    C= ' expr $A + $B '    

Simplification of Expressions

increment, decrement, etc. of a variable

shorthand expression    Complete expression I+ +      i=i+1i--    i=i-1i*=2    i=i* 2 I+ =2     i=i+2i-=2      i=i-2i%= 2     i=i%2

Attention:

i++: First participate in other operations, after the operation ++i: first operation, and then participate in other operations

Example:

i=1echo $ ((+ +i)) J=1echo $ ((J+ +))

self-increment of variables/Reduction Operations

using the Let command

Operation variable value, only operation, not output results to see the results, you need to use the echo command let: Only do the operation does not return the results of the calculation, for the self-plus and decrement operations

#!/bin/Bashi=  i-=2echo $ilet i-=2------------ -------I=ten let i+= 2echo $ilet i+ =2echo $i

Five, Shell operations