Linux - Do math operations in shell

转自 http://doc.dev.md/lsst/

To do math operations in shell use "expr", syntax is as follows  
Syntax: expr   op1   operator   op2

Where, op1 and op2 are any Integer Number (Number without decimal point) and operator can be:
+ Addition
- Subtraction
/ Division
% Modular, to find remainder For e.g. 20 / 3 = 6 , to find remainder 20 % 3 = 2, (Remember its integer calculation)
\* Multiplication （注意要有反斜线）

Note: space is required between number and operator