Linux Commands for Beginners lesson 19 -- expr,let commands

In this part,I will show you how to do some arithmetic calculation in Bash.

1.COMMAND:
      expr
  DESCRIPTION:
       Print  the  value of EXPRESSION to standard output.
  SYNOPSIS:
       expr EXPRESSION
       
Example:
root@piniheaven:~# expr 1 + 1
2
root@piniheaven:~# expr 2 - 1
1
root@piniheaven:~# expr 4 / 2
2
root@piniheaven:~# expr 2 \* 2  #Tip: when you want to do some multiplication,you should use backslash
4


2.COMMAND:
     let
 DESCRIPTION:
     carry out arithmetic operations on variables. 

Example:
root@piniheaven:~# let " val=(1+1)*2"  # will compute 2 times 2 and assign the result to the variable "val".
root@piniheaven:~# echo $val    #print variable val
4